View source for Formaldehyde

{{short description|Organic compound (H–CHO); simplest aldehyde}}
{{Redirect-distinguish|Methanal|Methanol|Menthol}}
{{Redirect|COH2|the video game|Company of Heroes 2}}
{{other uses}}
{{Chembox
| Watchedfields = changed
| verifiedrevid = 464368486
| Name = 
| ImageFile = 
| ImageFileL1 = Structural formula of formaldehyde.svg
| ImageClassL1 = skin-invert-image
| ImageFileL1_Ref = {{chemboximage|correct|??}}
| ImageNameL1 = Structural formula of formaldehyde (with hydrogens)
| ImageFileR1 = Formaldehyde-3D-vdW.png
| ImageClassR1 = bg-transparent
| ImageFileR1_Ref = {{chemboximage|correct|??}}
| ImageNameR1 = Spacefill model of formaldehyde
| ImageFile2 = Formaldehyde-3D-balls-A.png
| ImageClass2 = bg-transparent
| ImageFile2_Ref = {{chemboximage|correct|??}}
| ImageSize2 = 121
| ImageName2 = Ball and stick model of formaldehyde
| PIN = Formaldehyde<ref name=iupac2013>{{cite book | title = Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 908 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter}}</ref>
| SystematicName = Methanal<ref name=iupac2013/>
| OtherNames = {{Unbulleted list|Methyl aldehyde|[[Methylene glycol]] (diol forms in aqueous solution)|Methylene oxide|Formalin (aqueous solution)|Formol|Carbonyl hydride|Methanone|Oxomethane|Formic aldehyde}}
| IUPACName = 
| Section1 = {{Chembox Identifiers
| IUPHAR_ligand = 4196
| CASNo=50-00-0
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem=712
| ChemSpiderID=692
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| UNII=1HG84L3525
| UNII_Ref = {{fdacite|correct|FDA}}
| EINECS=200-001-8
| UNNumber=2209
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank=DB03843
| KEGG=D00017
| KEGG_Ref = {{keggcite|correct|kegg}}
| MeSHName=Formaldehyde
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI=16842
| ChEMBL=1255
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| RTECS=LP8925000
| Beilstein=1209228
| Gmelin=445
| 3DMet=B00018
| SMILES=C=O
| StdInChI=1S/CH2O/c1-2/h1H2
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| InChI=1/CH2O/c1-2/h1H2
| StdInChIKey=WSFSSNUMVMOOMR-UHFFFAOYSA-N
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| InChIKey=WSFSSNUMVMOOMR-UHFFFAOYAT
}}
| Section2 = {{Chembox Properties
| Properties_ref =<ref>{{RubberBible62nd|pages=C–301, E–61}}</ref>
| C=1 | H=2 | O=1
| Appearance=Colorless gas
| Density=0.8153 g/cm<sup>3</sup> (−20&nbsp;°C)<ref name=ipcs>{{cite web | title = SIDS Initial Assessment Report | url = http://www.inchem.org/documents/sids/sids/FORMALDEHYDE.pdf | publisher = International Programme on Chemical Safety | access-date = 2019-04-21 | archive-url = https://web.archive.org/web/20190328010406/http://www.inchem.org/documents/sids/sids/FORMALDEHYDE.pdf | archive-date = 2019-03-28 }}</ref> (liquid)
| MeltingPtC=-92
| BoilingPtC=-19
| BoilingPt_ref = <ref name=ipcs/>
| pKa = 13.27 (hydrate)<ref>
{{cite web | url = https://pubchem.ncbi.nlm.nih.gov/compound/formaldehyde#section=Odor-Threshold | title = PubChem Compound Database; CID=712 | publisher = National Center for Biotechnology Information | access-date = 2017-07-08 | archive-url = https://web.archive.org/web/20190412235321/https://pubchem.ncbi.nlm.nih.gov/compound/formaldehyde#section=Odor-Threshold | archive-date = 2019-04-12 | url-status = live}}</ref><ref>{{cite web | title = Acidity of aldehydes | url = http://chemistry.stackexchange.com/questions/12232/acidity-of-aldehydes | publisher = Chemistry Stack Exchange | access-date = 2019-04-21 | archive-url = https://web.archive.org/web/20180901112531/https://chemistry.stackexchange.com/questions/12232/acidity-of-aldehydes | archive-date = 2018-09-01 }}</ref>
| Solubility=400 g/L
| LogP=0.350
| Dipole= 2.330 D<ref>{{cite web | last1 = Nelson | first1 = R. D. Jr. | last2 = Lide | first2 = D. R. | last3 = Maryott | first3 = A. A. | year = 1967 | title = Selected Values of electric dipole moments for molecules in the gas phase (NSRDS-NBS10) | url = https://nvlpubs.nist.gov/nistpubs/Legacy/NSRDS/nbsnsrds10.pdf | access-date = 2019-04-21 | archive-url = https://web.archive.org/web/20180608004619/https://nvlpubs.nist.gov/nistpubs/Legacy/NSRDS/nbsnsrds10.pdf | archive-date = 2018-06-08 | url-status = live}}</ref>
| VaporPressure = > 1 atm<ref>{{cite journal | last1 = Spence | first1 = Robert | last2 = Wild | first2 = William | year = 1935 | title = 114. The vapour-pressure curve of formaldehyde, and some related data | journal = Journal of the Chemical Society (Resumed) | pages = 506–509 | doi = 10.1039/jr9350000506}}</ref>
| MagSus = −18.6·10<sup>−6</sup> cm<sup>3</sup>/mol
}}
| Section3 = {{Chembox Structure
| MolShape=Trigonal planar
| PointGroup = C<sub>2v</sub>
}}
| Section4 = {{Chembox Thermochemistry
| Thermochemistry_ref = <ref name="CRC97">{{Cite book |title=CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data. |date=2016 |others=William M. Haynes, David R. Lide, Thomas J. Bruno |isbn=978-1-4987-5428-6 |edition=2016-2017, 97th |location=Boca Raton, Florida |oclc=930681942 }}</ref>
| HeatCapacity = 35.387&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup>
| Entropy = 218.760&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup>
| DeltaHform = −108.700&nbsp;kJ·mol<sup>−1</sup>
| DeltaGfree = −102.667&nbsp;kJ·mol<sup>−1</sup>
| DeltaHcombust = 571&nbsp;kJ·mol<sup>−1</sup>
 }}
| Section5 = 
| Section6 = {{Chembox Pharmacology
| ATCvet = yes
| ATCCode_prefix = P53
| ATCCode_suffix = AX19
}}
| Section7 = {{Chembox Hazards
| ExternalSDS =[https://www.fishersci.com/shop/msdsproxy?productName=F75P1GAL&productDescription=formaldehyde--by-weight-histological-fisher-chemical&catNo=F75P-1GAL&vendorId=VN00000001&storeId=10652 MSDS]([https://web.archive.org/web/20170918021414/https://www.fishersci.com/shop/msdsproxy?productName=F75P1GAL&productDescription=formaldehyde--by-weight-histological-fisher-chemical&catNo=F75P-1GAL&vendorId=VN00000001&storeId=10652 Archived])
| GHSPictograms = {{GHS06}}{{GHS05}}{{GHS08}}<ref name="GESTIS">{{GESTIS|ZVG=10520 |CAS=50-00-0 |Name=Formaldehyde |Date=13 March 2020}}</ref>
| GHSSignalWord = '''Danger'''
| HPhrases = {{H-phrases|301+311+331|314|317|335|341|350|370}}<ref name=GESTIS/>
| PPhrases = {{P-phrases|201|280|303+361+353|304+340+310|305+351+338|308+310}}<ref name=GESTIS/>
| NFPA-H=4
| NFPA-F=4 <!-- as gas; common aqueous solution (37%) is only F=2 -->
| NFPA-R=0
| NFPA-S=COR
| FlashPtC = 64
| AutoignitionPtC = 430
| ExploLimits =7–73%
| LD50=100 mg/kg (oral, rat)<ref>{{cite web | title = Substance Name: Formaldehyde [USP] | url = https://pubchem.ncbi.nlm.nih.gov/#tab/sidsrcname=ChemIDplus&query=50-00-0&input_type=text | website= ChemlDplus|publisher= US National Library of Medicine | archive-url = https://web.archive.org/web/20170918063725/https://chem.nlm.nih.gov/chemidplus/rn/50-00-0 | archive-date = 2017-09-18 | url-status=live}}</ref>
| PEL = TWA 0.75 ppm ST 2 ppm (as formaldehyde and formalin)<ref name=PGCH>{{PGCH|0293}}</ref><ref>{{PGCH|0294}}</ref>
| IDLH = Ca [20 ppm]<ref name=PGCH/>
| REL = Ca TWA 0.016 ppm C 0.1 ppm [15-minute]<ref name=PGCH/>
| LC50 = 333 ppm (mouse, 2&nbsp;[[hour|h]])<br />815 ppm (rat, 30&nbsp;min)<ref name=IDLH>{{IDLH|50000|Formaldehyde}}</ref>
| LCLo = 333 ppm (cat, 2&nbsp;[[hour|h]])<ref name=IDLH/>
}}
| Section8 = {{Chembox Related
| OtherFunction_label =[[aldehyde]]s
| OtherFunction = {{ubl|[[Acetaldehyde]]|[[Propionaldehyde]]|[[Butyraldehyde]]|[[Pentanal]]|[[Hexanal]]|[[Heptanal]]|[[Octanal]]|[[Nonanal]]|[[Decanal]]|[[Octadecanal]]}}
| OtherCompounds = {{ubl|[[Methanol]]|[[Formic acid]]|[[Methanimine]]|[[Ethylene]]|[[Phosgene]]|[[Carbonyl fluoride]]|[[Thioformaldehyde]]}}
}}
}}

'''Formaldehyde''' ({{IPAc-en|audio=En-us-Formaldehyde2.ogg|f|ɔːr|ˈ|m|æ|l|d|ɪ|h|aɪ|d}} {{respell|for|MAL|di|hide}}, {{IPAc-en|USalso|audio=En-us-Formaldehyde.ogg|f|ə|r|-}} {{respell|fər|-}}) ([[Preferred IUPAC name|systematic name]] '''methanal''') is an [[organic compound]] with the [[chemical formula]] {{chem2|CH2O}} and structure {{chem2|H2C\dO}}. The compound is a pungent, colourless gas that [[Polymerization|polymerises]] spontaneously into [[paraformaldehyde]]. It is stored as aqueous solutions ('''formalin'''), which consists mainly of the hydrate CH<sub>2</sub>(OH)<sub>2</sub>. It is the simplest of the [[aldehyde]]s ({{chem2|R\sCHO}}). As a precursor to many other materials and chemical compounds, in 2006 the global production of formaldehyde was estimated at 12&nbsp;million tons per year.<ref>{{Cite book |last=Humans |first=IARC Working Group on the Evaluation of Carcinogenic Risks to |url=https://www.ncbi.nlm.nih.gov/books/NBK326456/ |title=Summary of Data Reported and Evaluation |date=2006 |publisher=International Agency for Research on Cancer |language=en |access-date=2023-03-06 |archive-date=2024-02-02 |archive-url=https://web.archive.org/web/20240202212813/https://www.ncbi.nlm.nih.gov/books/NBK326456/ |url-status=live}}</ref> It is mainly used in the production of industrial [[resin]]s, e.g., for [[particle board]] and [[coating]]s. 

Formaldehyde also occurs naturally. It is derived from the degradation of [[serine]], [[dimethylglycine]], and [[lipid]]s.  [[Demethylase]]s act by converting ''N''-methyl groups to formaldehyde.<ref>{{cite journal |doi=10.1038/s42004-019-0224-2 |title=How formaldehyde reacts with amino acids |date=2019 |last1=Kamps |first1=Jos J. A. G. |last2=Hopkinson |first2=Richard J. |last3=Schofield |first3=Christopher J. |last4=Claridge |first4=Timothy D. W. |journal=Communications Chemistry |volume=2 |issue=1 |page=126 |bibcode=2019CmChe...2..126K |doi-access=free }}</ref>

Formaldehyde is classified as a group 1 [[carcinogen]]{{refn|group=note|name=carcinogen|Formaldehyde is classified as a carcinogen, according to the [[United States Environmental Protection Agency|Environmental Protection Agency]], [[International Agency for Research on Cancer|International Agency for Research on Cancer (IARC)]], and U.S. National Toxicology Program.<ref name="cancer.gov">{{cite web|url=https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet|access-date=2023-09-21|archive-url=https://web.archive.org/web/20230920183106if_/https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet|archive-date=2023-09-20|title=Formaldehyde and Cancer Risk|date=10 June 2011}}</ref>}}<ref>{{cite book |last1=Zhang |first1=Luoping |title=Formaldehyde: Exposure, Toxicity and Health Effects |date=2018 |publisher=Royal Society of Chemistry, The |location=Cambridge |isbn=978-1-78262-973-3 |edition=1st |chapter=CH 5. Formaldehyde Carcinogenesis}}</ref> and can cause respiratory and skin [[irritation]] upon exposure.<ref name="cancer.gov" />

==Forms==
Formaldehyde is more complicated than many simple carbon compounds in that it adopts several diverse forms. These compounds can often be used interchangeably and can be interconverted.
*Molecular formaldehyde. A colorless gas with a characteristic pungent, irritating odor. It is stable at about 150&nbsp;°C, but it polymerizes when condensed to a liquid.
*[[1,3,5-Trioxane]], with the formula (CH<sub>2</sub>O)<sub>3</sub>. It is a white solid that dissolves without degradation in organic solvents. It is a [[trimer (chemistry)|trimer]] of molecular formaldehyde.
*[[Paraformaldehyde]], with the formula HO(CH<sub>2</sub>O)<sub>n</sub>H. It is a white solid that is insoluble in most solvents.
*[[Methanediol]], with the formula CH<sub>2</sub>(OH)<sub>2</sub>. This compound also exists in equilibrium with various [[oligomer]]s (short polymers), depending on the concentration and temperature. A saturated water solution, of about 40% formaldehyde by volume or 37% by mass, is called "100% formalin".

A small amount of [[stabilizer (chemistry)|stabilizer]], such as [[methanol]], is usually added to suppress [[oxidation]] and [[polymerization]]. A typical commercial-grade formalin may contain 10–12% methanol in addition to various metallic impurities.

"Formaldehyde" was first used as a [[generic trademark]] in 1893 following a previous trade name, "formalin".<ref>{{Citation | title = Formalin | publisher = Merriam-Webster, Inc. | url = https://www.merriam-webster.com/dictionary/formalin | date = 15 January 2020 | access-date = 18 February 2020 | archive-date = 18 April 2020 | archive-url = https://web.archive.org/web/20200418141055/https://www.merriam-webster.com/dictionary/formalin | url-status = live}}</ref>
<gallery |centered="" caption="Main forms of formaldehyde">
Structural formula of formaldehyde.svg|Monomeric formaldehyde (subject of this article)
File:S-Trioxane.svg|Trioxane is a stable cyclic trimer of formaldehyde.
File:Paraformaldehyd.svg|Paraformaldehyde is a common form of formaldehyde for industrial applications.
Methanediol-2D.png|Methanediol, the predominant species in dilute aqueous solutions of formaldehyde
</gallery>

===Structure and bonding ===
The formaldehyde molecule is Y-shaped and its [[molecular symmetry]] belongs to the [[Molecular symmetry#Common point groups|''C''<sub>2v</sub> point group]].<ref>{{Greenwood&Earnshaw2nd|page=1291}}</ref> The precise [[molecular geometry]] of gaseous formaldehyde has been determined by [[gas electron diffraction]]<ref name="Wells">{{cite book | first1 = A. F. | last1 = Wells | title = Structural Inorganic Chemistry | edition = 5th | year = 1984 | publisher = Oxford University Press | isbn = 978-0-19-965763-6 | pages = 915–917, 926}}</ref><ref name="CKIM">{{cite journal | title = Electron Diffraction Studies of Formaldehyde, Acetaldehyde and Acetone | first1 = Kato | last1 = Chuichi | first2 = Konaka | last2 = Shigehiro | first3 = Iijima | last3 = Takao | first4 = Kimura | last4 = Masao | journal = [[Bulletin of the Chemical Society of Japan|Bull. Chem. Soc. Jpn.]] | year = 1969 | volume = 42 | issue = 8 | pages = 2148–2158 | doi = 10.1246/bcsj.42.2148 | doi-access = free}}</ref> and [[microwave spectroscopy]].<ref name="CRC">{{cite book | title = [[CRC Handbook of Chemistry and Physics]] | edition = 93rd | publisher = [[CRC Press]] | year = 2012 | editor = William M. Haynes | pages = 9–39 | isbn = 978-1-4398-8050-0}}</ref><ref name="Duncan">{{cite journal | title = The ground-state average and equilibrium structures of formaldehyde and ethylene | first = J. L. | last = Duncan | journal = [[Molecular Physics (journal)|Mol. Phys.]] | year = 1974 | volume = 28 | issue = 5 | pages = 1177–1191 | doi = 10.1080/00268977400102501 | bibcode = 1974MolPh..28.1177D}}</ref> The [[bond length]]s are 1.21 [[Ångstrom|Å]] for the [[carbon–oxygen bond]]<ref name="Wells" /><ref name="CKIM" /><ref name="CRC" /><ref name="Duncan" /><ref name="March">{{cite book | first1 = Michael B. | last1 = Smith | first2 = Jerry | last2 = March | title = March's Advanced Organic Chemistry | publisher = John Wiley & Sons | year = 2007 | edition=6th | isbn = 978-0-471-72091-1 | pages = 24–25, 335}}</ref> and around 1.11 Å for the [[carbon–hydrogen bond]],<ref name="Wells" /><ref name="CKIM" /><ref name="CRC" /><ref name="Duncan" /> while the H–C–H [[bond angle]] is 117°,<ref name="CRC" /><ref name="Duncan" /> close to the 120° angle found in an ideal [[trigonal planar molecular geometry|trigonal planar molecule]].<ref name="Wells" /> Some [[Excited state|excited electronic states]] of formaldehyde are [[Trigonal pyramidal molecular geometry|pyramidal]] rather than planar as in the [[ground state]].<ref name="March" />

==Occurrence==

=== Atmospheric ===

==== Sources ====
Formaldehyde (HCHO) is introduced into the atmosphere via primary emission and secondary formation.<ref>{{Cite journal|title=Characteristics and Sources of Atmospheric Formaldehyde in a Coastal City in Southeast China|journal=Atmosphere|date=2025-09-26|issn=2073-4433|pages=1131|volume=16|issue=10|doi=10.3390/atmos16101131|language=en|first1=Yiling|last1=Lin|first2=Qiaoling|last2=Chen|first3=Youwei|last3=Hong|first4=Yanting|last4=Chen|first5=Liqian|last5=Yin|first6=Jinfang|last6=Chen|first7=Gongren|last7=Hu|first8=Dan|last8=Liao|first9=Ruilian|last9=Yu |bibcode=2025Atmos..16.1131L |doi-access=free }}</ref> Primary sources of atmospheric HCHO include direct biogenic emissions from vegetation and biomass burning, as well as anthropogenic emissions from vehicles, industrial activities, and coal combustion. <ref>{{Cite journal|title=Primary and secondary sources of ambient formaldehyde in the Yangtze River Delta based on Ozone Mapping and Profiler Suite (OMPS) observations|url=https://acp.copernicus.org/articles/19/6717/2019/|journal=Atmospheric Chemistry and Physics|date=2019-05-20|issn=1680-7324|pages=6717–6736|volume=19|issue=10|doi=10.5194/acp-19-6717-2019|language=en|first1=Wenjing|last1=Su|first2=Cheng|last2=Liu|first3=Qihou|last3=Hu|first4=Shaohua|last4=Zhao|first5=Youwen|last5=Sun|first6=Wei|last6=Wang|first7=Yizhi|last7=Zhu|first8=Jianguo|last8=Liu|first9=Jhoon|last9=Kim |bibcode=2019ACP....19.6717S |doi-access=free }}</ref><ref>{{Cite journal|title=Validation of formaldehyde products from three satellite retrievals (OMI SAO, OMPS-NPP SAO, and OMI BIRA) in the marine atmosphere with four seasons of Atmospheric Tomography Mission (ATom) aircraft observations|url=https://amt.copernicus.org/articles/18/1/2025/|journal=Atmospheric Measurement Techniques|date=2025-01-03|issn=1867-8548|pages=1–16|volume=18|issue=1|doi=10.5194/amt-18-1-2025|language=en|first1=Jin|last1=Liao|first2=Glenn M.|last2=Wolfe|first3=Alexander E.|last3=Kotsakis|first4=Julie M.|last4=Nicely|first5=Jason M.|last5=St. Clair|first6=Thomas F.|last6=Hanisco|first7=Gonzalo|last7=González Abad|first8=Caroline R.|last8=Nowlan|first9=Zolal|last9=Ayazpour|first10=Isabelle|last10=De Smedt|first11=Eric C.|last11=Apel|first12=Rebecca S.|last12=Hornbrook |bibcode=2025AMT....18....1L |doi-access=free }}</ref> The large majority of atmospheric HCHO is secondary, produced by radical-driven oxidation of [[Methane|methane (CH<sub>4</sub>)]] and non-methane [[Volatile organic compound|volatile organic compounds (VOCs)]] rather than direct emissions. <ref>{{Cite journal|title=Measurement report: Production and loss of atmospheric formaldehyde at a suburban site of Shanghai in summertime|url=https://acp.copernicus.org/articles/23/2997/2023/|journal=Atmospheric Chemistry and Physics|date=2023-03-07|issn=1680-7324|pages=2997–3014|volume=23|issue=5|doi=10.5194/acp-23-2997-2023|language=en|first1=Yizhen|last1=Wu|first2=Juntao|last2=Huo|first3=Gan|last3=Yang|first4=Yuwei|last4=Wang|first5=Lihong|last5=Wang|first6=Shijian|last6=Wu|first7=Lei|last7=Yao|first8=Qingyan|last8=Fu|first9=Lin|last9=Wang |bibcode=2023ACP....23.2997W |doi-access=free }}</ref> Secondary production from CH<sub>4</sub> oxidation dominates in remote and marine environments.  In contrast, oxidation of biogenic and anthropogenic VOCs is the main source of HCHO in continental regions. <ref>{{Cite journal|title=Contributions to local- and regional-scale formaldehyde concentrations|url=https://acp.copernicus.org/articles/19/8363/2019/|journal=Atmospheric Chemistry and Physics|date=2019-07-02|issn=1680-7324|pages=8363–8381|volume=19|issue=13|doi=10.5194/acp-19-8363-2019|language=en|first1=Lucas A. J.|last1=Bastien|first2=Nancy J.|last2=Brown|first3=Robert A.|last3=Harley |bibcode=2019ACP....19.8363B |doi-access=free }}</ref> Vegetation emits large amounts of [[isoprene]], which is an important natural precursor of tropospheric formaldehyde over many land regions.<ref>{{Cite journal |last1=Guenther|first1=A.|last2=Karl|first2=T.|last3=Harley|first3=P.|last4=Wiedinmyer|first4=C.|last5=Palmer|first5=P. I.|last6=Geron|first6=C.|date=2006-08-02|title=Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)|url=https://acp.copernicus.org/articles/6/3181/2006/|journal=Atmospheric Chemistry and Physics|language=en|volume=6|issue=11|pages=3181–3210|doi=10.5194/acp-6-3181-2006|bibcode=2006ACP.....6.3181G |doi-access=free |issn=1680-7324}}</ref><ref name=":1">{{Cite journal |last1=Abbot|first1=Dorian S.|last2=Palmer|first2=Paul I.|last3=Martin|first3=Randall V.|last4=Chance|first4=Kelly V.|last5=Jacob|first5=Daniel J.|last6=Guenther|first6=Alex|date=September 2003|title=Seasonal and interannual variability of North American isoprene emissions as determined by formaldehyde column measurements from space|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2003GL017336|journal=Geophysical Research Letters|language=en|volume=30|issue=17|article-number=2003GL017336 |doi=10.1029/2003GL017336|bibcode=2003GeoRL..30.1886A |issn=0094-8276}}</ref>

==== Role in atmospheric chemistry ====
As a short-lived but very reactive [[Carbonyl group|carbonyl compound]], HCHO plays an important role in the oxidation chemistry of the [[troposphere]]. It is a key source of odd-hydrogen radicals (HO<sub>x</sub> = OH + HO<sub>2</sub>) that help to sustain the atmosphere’s oxidative capacity. <ref>{{Cite journal |last1=Welsh|first1=Blair A.|last2=Corrigan|first2=Maggie E.|last3=Assaf|first3=Emmanuel|last4=Nauta|first4=Klaas|last5=Sebastianelli|first5=Paolo|last6=Jordan|first6=Meredith J. T.|last7=Fittschen|first7=Christa|last8=Kable|first8=Scott H.|date=October 2023|title=Photophysical oxidation of HCHO produces HO2 radicals|url=https://www.nature.com/articles/s41557-023-01272-4|journal=Nature Chemistry|language=en|volume=15|issue=10|pages=1350–1357|doi=10.1038/s41557-023-01272-4|pmid=37414879 |issn=1755-4330|hdl=1959.4/unsworks_84342|hdl-access=free}}</ref> HCHO is also considered an important ozone precursor. <ref>{{Cite journal |last1=Luecken|first1=D. J.|last2=Napelenok|first2=S. L.|last3=Strum|first3=M.|last4=Scheffe|first4=R.|last5=Phillips|first5=S.|date=2018-04-17|title=Sensitivity of Ambient Atmospheric Formaldehyde and Ozone to Precursor Species and Source Types Across the United States|journal=Environmental Science & Technology|language=en|volume=52|issue=8|pages=4668–4675|doi=10.1021/acs.est.7b05509|issn=0013-936X|pmc=6147010|pmid=29570979 |bibcode=2018EnST...52.4668L }}</ref>

HCHO removal in the troposphere occurs primarily through [[photodissociation]]. This occurs through two main pathways: molecular and radical forming channels,{{huh|date=November 2025}} the threshold wavelengths{{huh|date=November 2025}} for which are given in parentheses. <ref name=":3">{{Cite journal |last1=Carbajo|first1=Paula Gorrotxategi|last2=Smith|first2=Shona C.|last3=Holloway|first3=Anne-Louise|last4=Smith|first4=Carina A.|last5=Pope|first5=Francis D.|last6=Shallcross|first6=Dudley E.|last7=Orr-Ewing|first7=Andrew J.|date=2008-12-04|title=Ultraviolet Photolysis of HCHO: Absolute HCO Quantum Yields by Direct Detection of the HCO Radical Photoproduct|url=https://pubs.acs.org/doi/10.1021/jp8070508|journal=The Journal of Physical Chemistry A|language=en|volume=112|issue=48|pages=12437–12448|doi=10.1021/jp8070508|pmid=18998660 |bibcode=2008JPCA..11212437C |issn=1089-5639|url-access=subscription}}</ref>

: Molecular: <chem>HCHO + hv  -> H2 + CO (\lambda < 360 nm)</chem>
: Radical: <chem>HCHO + hv  -> H + HCO (\lambda < 330 nm)</chem>

The <chem>H</chem> and <chem>HCO</chem> radicals react with the atmospheric <chem>O2</chem> to form hydroperoxyl (<chem>HO2</chem>) radicals, giving a net radical channel of:

: <chem>HCHO + hv + 2O2 -> 2 HO2 + CO</chem>

In addition, in the presence of [[NOx|NO<sub>x</sub>]] and sunlight, HCHO contributes to [[tropospheric ozone]] formation, a key component of photochemical smog. <ref>{{Cite journal |last1=Nussbaumer|first1=Clara M.|last2=Crowley|first2=John N.|last3=Schuladen|first3=Jan|last4=Williams|first4=Jonathan|last5=Hafermann|first5=Sascha|last6=Reiffs|first6=Andreas|last7=Axinte|first7=Raoul|last8=Harder|first8=Hartwig|last9=Ernest|first9=Cheryl|last10=Novelli|first10=Anna|last11=Sala|first11=Katrin|last12=Martinez|first12=Monica|last13=Mallik|first13=Chinmay|last14=Tomsche|first14=Laura|last15=Plass-Dülmer|first15=Christian|date=2021-12-17|title=Measurement report: Photochemical production and loss rates of formaldehyde and ozone across Europe|url=https://acp.copernicus.org/articles/21/18413/2021/|journal=Atmospheric Chemistry and Physics|language=en|volume=21|issue=24|pages=18413–18432|doi=10.5194/acp-21-18413-2021|bibcode=2021ACP....2118413N |doi-access=free |issn=1680-7324}}</ref>

: <chem>HCHO + hv + 2O2 -> H2O + CO + O3</chem>

==== Remote monitoring ====

[[Spectrometer]]s on [[earth observation satellite]]s allow monitoring of formaldehyde in the [[troposphere]]. Using [[ultraviolet–visible spectroscopy]], instruments detect the absorption features in sunlight reflected by the Earth and use [[differential optical absorption spectroscopy]] to calculate vertical column densities. <ref>{{Cite journal |last1=Zhu|first1=Lei|last2=Jacob|first2=Daniel J.|last3=Kim|first3=Patrick S.|last4=Fisher|first4=Jenny A.|last5=Yu|first5=Karen|last6=Travis|first6=Katherine R.|last7=Mickley|first7=Loretta J.|last8=Yantosca|first8=Robert M.|last9=Sulprizio|first9=Melissa P.|last10=De Smedt|first10=Isabelle|last11=González Abad|first11=Gonzalo|last12=Chance|first12=Kelly|last13=Li|first13=Can|last14=Ferrare|first14=Richard|last15=Fried|first15=Alan|date=2016-11-01|title=Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC 4 RS aircraft observations over the southeast US|journal=Atmospheric Chemistry and Physics|language=en|volume=16|issue=21|pages=13477–13490|doi=10.5194/acp-16-13477-2016|doi-access=free |issn=1680-7324|pmc=5880299|pmid=29619044}}</ref> Near-global maps of tropospheric HCHO with daily coverage and kilometer-scale spatial resolution are provided by the [[Ozone monitoring instrument|OMI]] instrument on [[Aura (satellite)|Aura]], the GOME-2 instrument on [[MetOp]], and the newer TROPOMI sensor on [[Sentinel-5 Precursor|Sentinel-5P]]. <ref>{{Cite journal |last1=De Smedt|first1=I.|last2=Stavrakou|first2=T.|last3=Hendrick|first3=F.|last4=Danckaert|first4=T.|last5=Vlemmix|first5=T.|last6=Pinardi|first6=G.|last7=Theys|first7=N.|last8=Lerot|first8=C.|last9=Gielen|first9=C.|last10=Vigouroux|first10=C.|last11=Hermans|first11=C.|last12=Fayt|first12=C.|last13=Veefkind|first13=P.|last14=Müller|first14=J.-F.|last15=Van Roozendael|first15=M.|date=2015-11-10|title=Diurnal, seasonal and long-term variations of global formaldehyde columns inferred from combined OMI and GOME-2 observations|url=https://acp.copernicus.org/articles/15/12519/2015/|journal=Atmospheric Chemistry and Physics|language=en|volume=15|issue=21|pages=12519–12545|doi=10.5194/acp-15-12519-2015|bibcode=2015ACP....1512519D |doi-access=free |issn=1680-7324}}</ref> Regional maps with hourly coverage over North America are available from the TEMPO instrument on [[Intelsat 40e]]. <ref>{{Cite journal |last1=Zoogman|first1=P.|last2=Liu|first2=X.|last3=Suleiman|first3=R.M.|last4=Pennington|first4=W.F.|last5=Flittner|first5=D.E.|last6=Al-Saadi|first6=J.A.|last7=Hilton|first7=B.B.|last8=Nicks|first8=D.K.|last9=Newchurch|first9=M.J.|last10=Carr|first10=J.L.|last11=Janz|first11=S.J.|last12=Andraschko|first12=M.R.|last13=Arola|first13=A.|last14=Baker|first14=B.D.|last15=Canova|first15=B.P.|date=January 2017|title=Tropospheric emissions: Monitoring of pollution (TEMPO)|journal=Journal of Quantitative Spectroscopy and Radiative Transfer|language=en|volume=186|pages=17–39|doi=10.1016/j.jqsrt.2016.05.008|pmc=7430511|pmid=32817995 |bibcode=2017JQSRT.186...17Z }}</ref><ref>{{Cite journal |last1=Jin|first1=Xiaomeng|last2=Yang|first2=Yohan|last3=Gonzalez Abad|first3=Gonzalo|last4=Nowlan|first4=Caroline|last5=Liu|first5=Xiong|date=2025-07-28|title=Observing the Diurnal Variations of Ozone-NO x -VOC Chemistry Over the U.S. From the Geostationary TEMPO Instrument|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL116394|journal=Geophysical Research Letters|language=en|volume=52|issue=14|article-number=e2025GL116394 |doi=10.1029/2025GL116394|issn=0094-8276|doi-access=free}}</ref>

The close coupling between isoprene and formaldehyde has been widely used in top-down approaches that derive regional and global isoprene emissions from satellite measurements of tropospheric formaldehyde columns. <ref>{{Cite journal |last1=Palmer|first1=Paul I.|last2=Jacob|first2=Daniel J.|last3=Fiore|first3=Arlene M.|last4=Martin|first4=Randall V.|last5=Chance|first5=Kelly|last6=Kurosu|first6=Thomas P.|date=2003-03-27|title=Mapping isoprene emissions over North America using formaldehyde column observations from space|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2002JD002153|journal=Journal of Geophysical Research: Atmospheres|language=en|volume=108|issue=D6|article-number=2002JD002153 |doi=10.1029/2002JD002153|bibcode=2003JGRD..108.4180P |issn=0148-0227}}</ref><ref name=":2">{{Cite journal |last1=Millet|first1=Dylan B.|last2=Jacob|first2=Daniel J.|last3=Turquety|first3=Solène|last4=Hudman|first4=Rynda C.|last5=Wu|first5=Shiliang|last6=Fried|first6=Alan|last7=Walega|first7=James|last8=Heikes|first8=Brian G.|last9=Blake|first9=Donald R.|last10=Singh|first10=Hanwant B.|last11=Anderson|first11=Bruce E.|last12=Clarke|first12=Antony D.|date=2006-12-27|title=Formaldehyde distribution over North America: Implications for satellite retrievals of formaldehyde columns and isoprene emission|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005JD006853|journal=Journal of Geophysical Research: Atmospheres|language=en|volume=111|issue=D24|article-number=2005JD006853 |doi=10.1029/2005JD006853|bibcode=2006JGRD..11124S02M |issn=0148-0227}}</ref> These studies provide important constraints on the magnitude and spatial pattern of biogenic isoprene emissions. <ref name=":1" /><ref name=":2" /><ref>{{Cite journal |last1=Kaiser|first1=Jennifer|last2=Jacob|first2=Daniel J.|last3=Zhu|first3=Lei|last4=Travis|first4=Katherine R.|last5=Fisher|first5=Jenny A.|last6=González Abad|first6=Gonzalo|last7=Zhang|first7=Lin|last8=Zhang|first8=Xuesong|last9=Fried|first9=Alan|last10=Crounse|first10=John D.|last11=St. Clair|first11=Jason M.|last12=Wisthaler|first12=Armin|date=2018-04-23|title=High-resolution inversion of OMI formaldehyde columns to quantify isoprene emission on ecosystem-relevant scales: application to the southeast US|url=https://acp.copernicus.org/articles/18/5483/2018/|journal=Atmospheric Chemistry and Physics|language=en|volume=18|issue=8|pages=5483–5497|doi=10.5194/acp-18-5483-2018|bibcode=2018ACP....18.5483K |doi-access=free |issn=1680-7324|hdl=11603/18899|hdl-access=free}}</ref>

Processes in the upper [[Earth's atmosphere|atmosphere]] contribute more than 80% of the total formaldehyde in the environment.<ref>{{Cite journal |last1=Luecken |first1=D. J. |last2=Hutzell |first2=W. T. |last3=Strum |first3=M. L. |last4=Pouliot |first4=G. A. |date=2012-02-01 |title=Regional sources of atmospheric formaldehyde and acetaldehyde, and implications for atmospheric modeling |url=https://www.sciencedirect.com/science/article/pii/S1352231011010508 |journal=Atmospheric Environment |volume=47 |pages=477–490 |doi=10.1016/j.atmosenv.2011.10.005 |bibcode=2012AtmEn..47..477L |issn=1352-2310|url-access=subscription }}</ref> Formaldehyde is an intermediate in the oxidation (or [[combustion]]) of [[methane]], as well as of other carbon compounds, e.g. in [[forest fire]]s, [[automobile]] exhaust, and [[tobacco smoke]]. When produced in the atmosphere by the action of sunlight and [[oxygen]] on [[atmospheric methane]] and other [[hydrocarbon]]s, it becomes part of [[smog]]. Formaldehyde has also been detected in outer space.

=== Environmental exposure ===

Formaldehyde and its [[adducts]] are ubiquitous in nature. Food may contain formaldehyde at levels 1–100&nbsp;mg/kg.<ref>{{Cite book |title=Air Quality Guidelines |publisher=WHO Regional Office for Europe |year=2001 |edition=2nd |location=Copenhagen, Denmark |language=en |chapter=Chapter 5.8 Formaldehyde |chapter-url=https://intranet.euro.who.int/__data/assets/pdf_file/0014/123062/AQG2ndEd_5_8Formaldehyde.pdf |access-date=2023-02-18 |archive-date=2023-02-18 |archive-url=https://web.archive.org/web/20230218053951/https://intranet.euro.who.int/__data/assets/pdf_file/0014/123062/AQG2ndEd_5_8Formaldehyde.pdf |url-status=live}}</ref> Formaldehyde, formed in the metabolism of the amino acids [[serine]] and [[threonine]], is found in the bloodstream of humans and other primates at concentrations of approximately 50&nbsp;[[micromolar]].<ref name=Chang>{{cite journal |doi=10.1126/science.abp9201 |title=Formaldehyde regulates ''S'' -adenosylmethionine biosynthesis and one-carbon metabolism |date=2023 |last1=Pham |first1=Vanha N. |last2=Bruemmer |first2=Kevin J. |last3=Toh |first3=Joel D. W. |last4=Ge |first4=Eva J. |last5=Tenney |first5=Logan |last6=Ward |first6=Carl C. |last7=Dingler |first7=Felix A. |last8=Millington |first8=Christopher L. |last9=Garcia-Prieto |first9=Carlos A. |last10=Pulos-Holmes |first10=Mia C. |last11=Ingolia |first11=Nicholas T. |last12=Pontel |first12=Lucas B. |last13=Esteller |first13=Manel |last14=Patel |first14=Ketan J. |last15=Nomura |first15=Daniel K. |last16=Chang |first16=Christopher J. |journal=Science |volume=382 |issue=6670 |article-number=eabp9201 |pmid=37917677 |bibcode=2023Sci...382P9201P |s2cid=264935787|pmc=11500418 }}</ref> Experiments in which animals are exposed to an atmosphere containing isotopically labeled formaldehyde have demonstrated that even in deliberately exposed animals, the majority of formaldehyde-DNA adducts found in non-respiratory tissues are derived from endogenously produced formaldehyde.<ref>{{cite journal |doi=10.1093/toxsci/kfq371 |title=Endogenous versus Exogenous DNA Adducts: Their Role in Carcinogenesis, Epidemiology, and Risk Assessment |year=2011 |last1=Swenberg |first1=J. A. |last2=Lu |first2=K. |last3=Moeller |first3=B. C. |last4=Gao |first4=L. |last5=Upton |first5=P. B. |last6=Nakamura |first6=J. |last7=Starr |first7=T. B. |journal=Toxicological Sciences |volume=120 |issue=Suppl 1 |pages=S130–S145 |pmid=21163908 |pmc=3043087}}</ref>

Formaldehyde does not accumulate in the environment, because it is broken down within a few hours by sunlight or by bacteria present in soil or water. Humans metabolize formaldehyde quickly, converting it to [[formic acid]].<ref>{{cite press release | date = 2014-01-29 | title = Formaldehyde Is Biodegradable, Quickly Broken Down in the Air By Sunlight or By Bacteria in Soil or Water | url = https://www.americanchemistry.com/Media/PressReleasesTranscripts/ACC-news-releases/Formaldehyde-Is-Biodegradable.html | publisher = Formaldehyde Panel of the American Chemistry Council | access-date = 2017-04-22 | archive-url = https://web.archive.org/web/20190328042754/https://www.americanchemistry.com/Media/PressReleasesTranscripts/ACC-news-releases/Formaldehyde-Is-Biodegradable.html | archive-date = 2019-03-28 }}</ref><ref>{{Cite web |date=2019-03-28 |title=Toxicological Profile for Formaldehyde |url=https://www.atsdr.cdc.gov/ToxProfiles/tp111.pdf |archive-url=https://web.archive.org/web/20190328010414/https://www.atsdr.cdc.gov/ToxProfiles/tp111.pdf |archive-date=2019-03-28 |access-date=2023-02-18}}</ref> It nonetheless presents [[#Safety|significant health concerns]], as a [[contaminant]].

===Interstellar formaldehyde===
{{Main|Interstellar formaldehyde}}

Formaldehyde appears to be a useful probe in astrochemistry due to prominence of the 1<sub>10</sub>←1<sub>11</sub> and 2<sub>11</sub>←2<sub>12</sub> ''K''-doublet transitions. It was the first polyatomic [[Organic chemistry|organic]] molecule detected in the [[interstellar medium]].<ref>{{cite journal|last1=Zuckerman|first1=B.|last2=Buhl|first2=D.|last3=Palmer|first3=P.|last4=Snyder|first4=L. E.|year=1970|title=Observation of interstellar formaldehyde|journal=Astrophys. J.|volume=160|pages=485–506|doi=10.1086/150449|bibcode=1970ApJ...160..485Z}}</ref> Since its initial detection in 1969, it has been observed in many regions of the [[Milky Way galaxy|galaxy]]. Because of the widespread interest in interstellar formaldehyde, it has been extensively studied, yielding new extragalactic sources.<ref name="mangum">{{cite journal|first1=Jeffrey G.|last1=Mangum|first2=Jeremy|last2=Darling|first3=Karl M.|last3=Menten|first4=Christian|last4=Henkel|s2cid=14035123|year=2008|title=Formaldehyde Densitometry of Starburst Galaxies|journal=Astrophys. J.|volume=673|issue=2|pages=832–46|doi=10.1086/524354|bibcode=2008ApJ...673..832M |arxiv = 0710.2115}}</ref> A proposed mechanism for the formation is the hydrogenation of CO ice:<ref name="Woon">{{cite journal|last=Woon|first=David E.|year=2002|title=Modeling Gas-Grain Chemistry with Quantum Chemical Cluster Calculations. I. Heterogeneous Hydrogenation of CO and H<sub>2</sub>CO on Icy Grain Mantles|journal=Astrophys. J.|volume=569|issue=1|pages=541–48|doi=10.1086/339279|bibcode=2002ApJ...569..541W |doi-access=free}}</ref>
: H + CO → HCO
: HCO + H → CH<sub>2</sub>O

[[Hydrogen cyanide|HCN]], [[Hydrogen isocyanide|HNC]], H<sub>2</sub>CO, and [[dust]] have also been observed inside the [[Coma (cometary)|comae]] of [[comet]]s [[C/2012 F6 (Lemmon)]] and [[Comet ISON|C/2012 S1 (ISON)]].<ref name="NASA-20140811">{{cite web |last1=Zubritsky |first1=Elizabeth |last2=Neal-Jones |first2=Nancy |title=RELEASE 14-038 - NASA's 3-D Study of Comets Reveals Chemical Factory at Work |url=http://www.nasa.gov/press/2014/august/goddard/nasa-s-3-d-study-of-comets-reveals-chemical-factory-at-work |date=11 August 2014 |work=[[NASA]] |access-date=12 August 2014 |archive-date=12 August 2014 |archive-url=https://web.archive.org/web/20140812210755/http://www.nasa.gov/press/2014/august/goddard/nasa-s-3-d-study-of-comets-reveals-chemical-factory-at-work |url-status=live}}</ref><ref name="AJL-20140811">{{cite journal |author=Cordiner, M.A. |s2cid=26277035 |title=Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array |date=11 August 2014 |journal=[[The Astrophysical Journal]] |volume=792 |number=1 |doi=10.1088/2041-8205/792/1/L2 |display-authors=etal |pages=L2 |bibcode=2014ApJ...792L...2C|arxiv=1408.2458}}</ref>

==Synthesis and industrial production==
===Laboratory synthesis===
Formaldehyde was discovered in 1859 by the Russian chemist [[Aleksandr Butlerov]] (1828–1886) when he attempted to synthesize methanediol ("methylene glycol") from [[iodomethane]] and [[silver oxalate]].<ref>{{Cite wikidata|Q55881565}}</ref> In his paper, Butlerov referred to formaldehyde as "dioxymethylen" (methylene dioxide) because his empirical formula for it was incorrect, as atomic weights were not precisely determined until the [[Karlsruhe Congress]].

The compound was identified as an aldehyde by [[August Wilhelm von Hofmann]], who first announced its production by passing methanol vapor in air over hot platinum wire.<ref>See: A. W. Hofmann (14 October 1867) [https://books.google.com/books?id=Vh4XAAAAYAAJ&pg=PA665 "Zur Kenntnis des Methylaldehyds"] ([Contributions] to our knowledge of methylaldehyde), ''Monatsbericht der Königlich Preussischen Akademie der Wissenschaften zu Berlin'' (Monthly Report of the Royal Prussian Academy of Sciences in Berlin), vol. 8, pages 665–669. Reprinted in:
*A.W. Hofmann, (1868) [https://books.google.com/books?id=RgEuAAAAIAAJ&pg=PA357 "Zur Kenntnis des Methylaldehyds"], ''Annalen der Chemie und Pharmacie'' (Annals of Chemistry and Pharmacy), vol. 145, no. 3, pages 357–361.
*A.W. Hofmann (1868) [https://books.google.com/books?id=4hNLAAAAYAAJ&pg=PA246 "Zur Kenntnis des Methylaldehyds"], ''Journal für praktische Chemie'' (Journal for Practical Chemistry), vol. 103, no. 1, pages 246–250.
However, it was not until 1869 that Hofmann determined the correct empirical formula of formaldehyde. See: A.W. Hofmann (5 April 1869) [https://books.google.com/books?id=58YAAAAAYAAJ&pg=PA362 "Beiträge zur Kenntnis des Methylaldehyds"], ''Monatsbericht der Königlich Preussischen Akademie der Wissenschaften zu Berlin'', vol. ?, pages 362–372. Reprinted in:
*{{cite journal | last1 = Hofmann | first1 = A.W. | year = 1869 | title = Beiträge zur Kenntnis des Methylaldehyds | url = https://books.google.com/books?id=2AIwAAAAIAAJ&pg=PA414 | journal = Journal für Praktische Chemie | volume = 107 | issue = 1| pages = 414–424 | doi=10.1002/prac.18691070161}}
*A.W. Hofmann (1869) "Beiträge zur Kenntnis des Methylaldehyds," ''Berichte der Deutschen Chemischen Gesellschaft'' (Reports of the German Chemical Society), vol. 2, pages 152–159.</ref><ref>{{cite book|first=J.|last=Read|title=Text-Book of Organic Chemistry|publisher=G Bell & Sons|location=London|year=1935}}</ref> With modifications, Hofmann's method remains the basis of the present day industrial route.

Solution routes to formaldehyde also entail oxidation of methanol or [[iodomethane]].<ref>{{cite journal|doi=10.1002/anie.200800991|title=A Simple, Rapid Method for the Preparation of &#91;11C&#93;Formaldehyde|year=2008|last1=Hooker|first1=Jacob M.|last2=Schönberger|first2=Matthias|last3=Schieferstein|first3=Hanno|last4=Fowler|first4=Joanna S.|journal=Angewandte Chemie International Edition|volume=47|issue=32|pages=5989–5992|pmid=18604787|pmc=2522306 |bibcode=2008ACIE...47.5989H }}</ref>

===Industry===
Formaldehyde is produced industrially by the catalytic oxidation of [[methanol]]. The most common catalysts are [[silver]] metal (i.e. the [[Fasil process|FASIL process]]), [[iron(III) oxide]],<ref>{{Cite journal |last1=Wang |first1=Chien-Tsung |last2=Ro |first2=Shih-Hung |date=2005-05-10 |title=Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation |url=https://www.sciencedirect.com/science/article/pii/S0926860X05001523 |journal=Applied Catalysis A: General |language=en |volume=285 |issue=1 |pages=196–204 |doi=10.1016/j.apcata.2005.02.029 |bibcode=2005AppCA.285..196W |issn=0926-860X|url-access=subscription }}</ref> iron molybdenum [[oxide]]s (e.g. iron(III) [[molybdate]]) with a [[molybdenum]]-enriched surface,<ref>{{Cite journal |last1=Dias |first1=Ana Paula Soares |last2=Montemor |first2=Fátima |author-link2=Maria de Fátima Montemor|last3=Portela |first3=Manuel Farinha |last4=Kiennemann |first4=Alain |date=2015-02-01 |title=The role of the suprastoichiometric molybdenum during methanol to formaldehyde oxidation over Mo–Fe mixed oxides |url=https://www.sciencedirect.com/science/article/pii/S1381116914004774 |journal=Journal of Molecular Catalysis A: Chemical |language=en |volume=397 |pages=93–98 |doi=10.1016/j.molcata.2014.10.022 |issn=1381-1169|url-access=subscription }}</ref> or [[vanadium pentoxide|vanadium]] [[oxide]]s. In the commonly used [[formox process]], methanol and oxygen react at c.&nbsp;250–400&nbsp;°C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the [[chemical equation]]:<ref name="Ullmann">{{Ullmann|doi=10.1002/14356007.a11_619|title=Formaldehyde|year=2000|last1=Reuss|first1=Günther|last2=Disteldorf|first2=Walter|last3=Gamer|first3=Armin Otto|last4=Hilt|first4=Albrecht|isbn=3527306730}}</ref>
:2{{nbsp}}CH<sub>3</sub>OH + O<sub>2</sub> → 2{{nbsp}}CH<sub>2</sub>O + 2{{nbsp}}H<sub>2</sub>O

The silver-based catalyst usually operates at a higher temperature, about 650&nbsp;°C. Two chemical reactions on it simultaneously produce formaldehyde: that shown above and the [[dehydrogenation]] reaction:
:CH<sub>3</sub>OH → CH<sub>2</sub>O + H<sub>2</sub>

In principle, formaldehyde could be generated by oxidation of [[methane]], but this route is not industrially viable because the methanol is more easily oxidized than methane.<ref name="Ullmann"/>

==Biochemistry==
Formaldehyde is produced via several enzyme-catalyzed routes.<ref name= Kamps/> Living beings, including humans, produce formaldehyde as part of their metabolism. Formaldehyde is key to several bodily functions (e.g. [[epigenetic]]s<ref name=Chang/>), but its amount must also be tightly controlled to avoid self-poisoning.<ref>{{cite journal |last1=Chen |first1=J |last2=Chen |first2=W |last3=Zhang |first3=J |last4=Zhao |first4=H |last5=Cui |first5=J |last6=Wu |first6=J |last7=Shi |first7=A |title=Dual effects of endogenous formaldehyde on the organism and drugs for its removal. |journal=Journal of Applied Toxicology |date=27 September 2023 |volume=44 |issue=6 |pages=798–817 |doi=10.1002/jat.4546 |pmid=37766419|s2cid=263125399}}</ref>

* [[Serine hydroxymethyltransferase]] can decompose [[serine]] into formaldehyde and [[glycine]], according to this reaction: HOCH<sub>2</sub>CH(NH<sub>2</sub>)CO<sub>2</sub>H → CH<sub>2</sub>O + H<sub>2</sub>C(NH<sub>2</sub>)CO<sub>2</sub>H.
* [[Methylotroph]]ic microbes convert methanol into formaldehyde and energy via [[methanol dehydrogenase]]: CH<sub>3</sub>OH → CH<sub>2</sub>O + 2e<sup>−</sup> + 2H<sup>+</sup>
* Other routes to formaldehyde include oxidative [[demethylation]]s, [[semicarbazide]]-sensitive [[amine oxidase]]s, [[dimethylglycine dehydrogenase]]s, [[lipid peroxidase]]s, [[P450 oxidase]]s, and ''N''-methyl group demethylases.<ref name= Kamps/>

Formaldehyde is catabolized by [[alcohol dehydrogenase]] [[ADH5]] and [[aldehyde dehydrogenase]] [[ALDH2]].<ref>{{cite journal |last1=Nakamura |first1=Jun |last2=Holley |first2=Darcy W. |last3=Kawamoto |first3=Toshihiro |last4=Bultman |first4=Scott J. |title=The failure of two major formaldehyde catabolism enzymes (ADH5 and ALDH2) leads to partial synthetic lethality in C57BL/6 mice |journal=Genes and Environment |date=December 2020 |volume=42 |issue=1 |page=21 |doi=10.1186/s41021-020-00160-4|doi-access=free |pmid=32514323 |pmc=7268536 |bibcode=2020GeneE..42...21N}}</ref>

==Organic chemistry==
Formaldehyde is a building block in the synthesis of many other compounds of specialised and industrial significance. It exhibits most of the chemical properties of other aldehydes but is more reactive.<ref>{{Cite book |last1=Cheng |first1=Chan |title=Formaldehyde: Chemistry, Applications and Role in Polymerization (Pollution Science, Technology and Abatement) |last2=Lu |first2=Feng |year=2012 |language=English}}</ref>

===Polymerization and hydration===
Monomeric CH<sub>2</sub>O is a gas and is rarely encountered in the laboratory.  Aqueous formaldehyde, unlike some other small aldehydes (which need specific conditions to oligomerize through [[aldol condensation]]) oligomerizes spontaneously at a common state. The trimer 1,3,5-trioxane, {{chem2|(CH2O)3}}, is a typical oligomer. Many cyclic [[oligomer]]s of other sizes have been isolated. Similarly, formaldehyde hydrates to give the geminal diol [[methanediol]], which condenses further to form hydroxy-terminated oligomers HO(CH<sub>2</sub>O)<sub>''n''</sub>H. The polymer is called [[paraformaldehyde]]. The higher concentration of formaldehyde—the more equilibrium shifts towards polymerization. Diluting with water or increasing the solution temperature, as well as adding alcohols (such as methanol or ethanol) lowers that tendency.

Gaseous formaldehyde polymerizes at active sites on vessel walls, but the mechanism of the reaction is unknown.<ref>{{Cite journal |last1=Boyles |first1=James G. |last2=Toby |first2=Sidney |date=June 1966 |title=The mechanism of the polymerization of gaseous formaldehyde |url=https://onlinelibrary.wiley.com/doi/10.1002/pol.1966.110040608 |journal=Journal of Polymer Science Part B: Polymer Letters |volume=4 |issue=6 |pages=411–415 |doi=10.1002/pol.1966.110040608 |bibcode=1966JPoSL...4..411B |access-date=2023-04-20 |archive-date=2023-04-20 |archive-url=https://web.archive.org/web/20230420083849/https://onlinelibrary.wiley.com/doi/10.1002/pol.1966.110040608 |url-status=live|url-access=subscription }}</ref> Small amounts of [[hydrogen chloride]], [[boron trifluoride]], or [[stannic chloride]] present in gaseous formaldehyde provide the catalytic effect and make the polymerization rapid.<ref>{{Cite journal |date=1951-03-07 |title=The catalyzed polymerization of gaseous formaldehyde |url=https://royalsocietypublishing.org/doi/10.1098/rspa.1951.0046 |journal=Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences |language=en |volume=205 |issue=1083 |pages=516–529 |doi=10.1098/rspa.1951.0046 |bibcode=1951RSPSA.205..516B |issn=0080-4630 |last1=Bevington |first1=J. C. |last2=Norrish |first2=R. G. W. |s2cid=95395629 |access-date=2023-04-20 |archive-date=2019-10-25 |archive-url=https://web.archive.org/web/20191025013353/https://royalsocietypublishing.org/doi/10.1098/rspa.1951.0046 |url-status=live|url-access=subscription }}</ref>

===[[Cross-link]]ing reactions===
Formaldehyde forms cross-links by first combining with a protein to form [[methylol]], which loses a water molecule to form a [[Schiff base]].<ref name="pmid26354429">{{cite journal | vauthors = Hoffman EA, Frey BL, Smith LM, Auble DT | title = Formaldehyde crosslinking: a tool for the study of chromatin complexes | journal = [[Journal of Biological Chemistry]] | volume = 290 | issue = 44 | pages = 26404–26411 | date = 2015 | pmid = 26354429 | pmc = 4646298  | doi = 10.1074/jbc.R115.651679 | bibcode = 2015JBiCh.29026404H | doi-access = free }}</ref> The Schiff base can then react with DNA or protein to create a cross-linked product.<ref name="pmid26354429" /> This reaction is the basis for the most common process of [[Fixation (histology)#Chemical fixation|chemical fixation]].

===Oxidation and reduction===
Formaldehyde is readily [[oxidation|oxidized]] by atmospheric oxygen into [[formic acid]]. For this reason, commercial formaldehyde is typically contaminated with formic acid. Formaldehyde can be hydrogenated into [[methanol]].

In the [[Cannizzaro reaction]], formaldehyde and [[base (chemistry)|base]] react to produce [[formic acid]] and methanol, a [[disproportionation reaction]].

===Hydroxymethylation and chloromethylation===
Formaldehyde reacts with many compounds, resulting in [[hydroxymethylation]]:
:X-H + CH<sub>2</sub>O → X-CH<sub>2</sub>OH{{nbsp|5}}(X = R<sub>2</sub>N, RC(O)NR', SH).

The resulting hydroxymethyl derivatives typically react further. Thus, amines give [[hexahydro-1,3,5-triazine]]s:
:3{{nbsp}}RNH<sub>2</sub> + 3{{nbsp}}CH<sub>2</sub>O → (RNCH<sub>2</sub>)<sub>3</sub> + 3{{nbsp}}H<sub>2</sub>O

Similarly, when combined with [[hydrogen sulfide]], it forms [[trithiane]]:<ref>{{OrgSynth|last1=Bost|first1=R. W.|last2=Constable|first2=E. W.|title=''sym''-Trithiane|prep=cv2p0610|volume=16|pages=81|year=1936|collvol=2|collvolpages=610}}</ref>
:3{{nbsp}}CH<sub>2</sub>O + 3{{nbsp}}H<sub>2</sub>S → (CH<sub>2</sub>S)<sub>3</sub> + 3{{nbsp}}H<sub>2</sub>O

In the presence of acids, it participates in [[electrophilic aromatic substitution]] reactions with [[aromatic compound]]s resulting in hydroxymethylated derivatives:
:ArH + CH<sub>2</sub>O → ArCH<sub>2</sub>OH
When conducted in the presence of hydrogen chloride, the product is the chloromethyl compound, as described in the [[Blanc chloromethylation]]. If the arene is electron-rich, as in phenols, elaborate condensations ensue. With 4-substituted phenols one obtains [[calixarenes]].<ref>{{OrgSynth|authorlink1=C. David Gutsche|last1=Gutsche|first1=C. D.|last2=Iqbal|first2=M.|title=''p-tert''-Butylcalix&#91;4&#93;arene|prep=cv8p0075|year=1993|collvol=8|collvolpages=75}}</ref> Phenol results in polymers.

===Other reactions===
Many amino acids react with formaldehyde.<ref name= Kamps>{{cite journal |doi=10.1038/s42004-019-0224-2 |title=How formaldehyde reacts with amino acids |date=2019 |last1=Kamps |first1=Jos J. A. G. |last2=Hopkinson |first2=Richard J. |last3=Schofield |first3=Christopher J. |last4=Claridge |first4=Timothy D. W. |journal=Communications Chemistry |volume=2 |issue=1 |page=126 |s2cid=207913561 |doi-access=free|bibcode=2019CmChe...2..126K }}</ref> Cysteine converts to [[thioproline]].

==Uses==

===Industrial applications===
Formaldehyde is a common precursor to more complex compounds and materials. In approximate order of decreasing consumption, products generated from formaldehyde include [[urea formaldehyde resin]], [[melamine resin]], [[phenol formaldehyde resin]], [[polyoxymethylene plastic]]s, [[1,4-butanediol]], and [[methylene diphenyl diisocyanate]].<ref name="Ullmann"/> The [[textile industry]] uses formaldehyde-based resins as [[Finishing (textiles)|finishers]] to make fabrics crease-resistant.<ref>{{cite web | title = Formaldehyde in Clothing and Textiles FactSheet | url = https://www.nicnas.gov.au/chemical-information/factsheets/chemical-name/formaldehyde-in-clothing-and-textiles | website = NICNAS | publisher = Australian National Industrial Chemicals Notification and Assessment Scheme | access-date = 2014-11-12 | date = 2013-05-01 | archive-url = https://web.archive.org/web/20190319234828/https://www.nicnas.gov.au/chemical-information/factsheets/chemical-name/formaldehyde-in-clothing-and-textiles | archive-date = 2019-03-19 }}</ref>

[[File:UFresinSyn.svg|thumb|340px|Two steps in formation of urea-formaldehyde resin, which is widely used in the production of particle board]]

When condensed with [[phenol]], [[urea]], or [[melamine]], formaldehyde produces, respectively, hard thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin. These polymers are permanent adhesives used in [[plywood]] and [[carpet]]ing. They are also foamed to make [[Thermal insulation|insulation]], or [[casting|cast]] into moulded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.

Formaldehyde is also a precursor to polyfunctional [[Alcohol (chemistry)|alcohol]]s such as [[pentaerythritol]], which is used to make [[paint]]s and [[explosive]]s. Other formaldehyde derivatives include methylene diphenyl diisocyanate, an important component in [[polyurethane]] paints and foams, and [[hexamine]], which is used in phenol-formaldehyde resins as well as the explosive [[RDX]].

Condensation with acetaldehyde affords [[pentaerythritol]], a chemical necessary in synthesizing [[PETN]], a high explosive:<ref>{{OrgSynth|first=H. B. J.|last=Schurink|title=Pentaerythritol|prep=cv1p0425|volume=4|pages=53|year= 1925|collvol=1|collvolpages=425}}</ref>
[[File:Pentaerythritol Synthesis.svg|600px|center]]

===Niche uses===
====Disinfectant and biocide====
An aqueous solution of formaldehyde can be useful as a disinfectant as it kills most [[bacteria]] and fungi (including their spores). It is used as an additive in vaccine manufacturing to inactivate toxins and pathogens.<ref>{{cite web | url = https://www.cdc.gov/vaccines/vac-gen/additives.htm | title = Ingredients of Vaccines - Fact Sheet | publisher = Center for Disease Control | access-date = 2018-08-04 | quote = Formaldehyde is used to inactivate bacterial products for toxoid vaccines, (these are vaccines that use an inactive bacterial toxin to produce immunity.) It is also used to kill unwanted viruses and bacteria that might contaminate the vaccine during production. Most formaldehyde is removed from the vaccine before it is packaged. | archive-url = https://web.archive.org/web/20190421020210/https://www.cdc.gov/vaccines/vac-gen/additives.htm | archive-date = 2019-04-21 | url-status = live}}</ref> [[Formaldehyde releaser]]s are used as biocides in personal care products such as cosmetics. Although present at levels not normally considered harmful, they are known to cause allergic [[contact dermatitis]] in certain sensitised individuals.<ref name="Formaldehyde Releasers" />

Aquarists use formaldehyde as a treatment for the parasites ''[[Ichthyophthirius multifiliis]]'' and ''[[Cryptocaryon irritans]]''.<ref>{{cite web|first=Ruth |last=Francis-Floyd |title=Use of Formalin to Control Fish Parasites |url=http://edis.ifas.ufl.edu/vm061 |publisher=Institute of Food and Agricultural Sciences, University of Florida |date=April 1996 |archive-url=https://web.archive.org/web/20120527111132/http://edis.ifas.ufl.edu/vm061 |archive-date=May 27, 2012}}</ref> Formaldehyde is one of the main disinfectants recommended for destroying [[anthrax]].<ref>{{Citation |title=Disinfection, decontamination, fumigation, incineration |date=2008 |url=https://www.ncbi.nlm.nih.gov/books/NBK310477/ |work=Anthrax in Humans and Animals. 4th edition |access-date=2023-11-20 |publisher=World Health Organization |language=en |archive-date=2022-07-06 |archive-url=https://web.archive.org/web/20220706223226/https://www.ncbi.nlm.nih.gov/books/NBK310477/ |url-status=live}}</ref>

Formaldehyde is also approved for use in the manufacture of animal feeds in the US. It is an antimicrobial agent used to maintain complete animal feeds or feed ingredients ''Salmonella'' negative for up to 21 days.<ref>{{cite web | date = 2019-04-19 | title = §573.460 Formaldehyde | url = http://www.ecfr.gov/cgi-bin/text-idx?SID=373e2ce8edf3f674e80eb9270a461c7d&mc=true&node=se21.6.573_1460&rgn=div8 | archive-url = https://web.archive.org/web/20170505205047/http://www.ecfr.gov/cgi-bin/text-idx?SID=373e2ce8edf3f674e80eb9270a461c7d&mc=true&node=se21.6.573_1460&rgn=div8 | archive-date = 2017-05-05 | publisher = U.S. Government Publishing Office | access-date = 2016-07-09}}</ref>

====Tissue fixative and embalming agent====
[[File:Steve O'Shea injecting formalin.jpg|thumb|Injecting a [[giant squid]] specimen with formalin for preservation]]
Formaldehyde preserves or [[Fixation (histology)|fixes]] tissue or cells. The process involves [[cross-link]]ing of primary [[amino group]]s. The European Union has banned the use of formaldehyde as a [[biocide]] (including [[embalming]]) under the [[Biocidal Products Directive]] (98/8/EC) due to its carcinogenic properties.<ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31998L0008:EN:HTML Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the placing of biocidal products on the market] {{Webarchive|url=https://web.archive.org/web/20080219232906/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31998L0008:EN:HTML |date=19 February 2008}}. ''OJEU'' L123, 24.04.1998, pp.&nbsp;1–63. ([http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1998L0008:20080926:EN:PDF consolidated version to 2008-09-26 (PDF)] {{Webarchive|url=https://web.archive.org/web/20100127033519/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1998L0008:20080926:EN:PDF |date=2010-01-27}})</ref><ref>[http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32003R2032:EN:HTML Commission Regulation (EC) No 2032/2003 of 4 November 2003 on the second phase of the 10-year work programme referred to in Article&nbsp;16(2) of Directive&nbsp;98/8/EC of the European Parliament and of the Council concerning the placing of biocidal products on the market, and amending Regulation&nbsp;(EC) No&nbsp;1896/2000] {{Webarchive|url=https://web.archive.org/web/20110612142224/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32003R2032:EN:HTML |date=12 June 2011}}. ''OJEU'' L307, 24.11.2003, p.&nbsp;1–96. ([http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:2003R2032:20070104:EN:PDF consolidated version to 2007-01-04 (PDF)] {{Webarchive|url=https://web.archive.org/web/20110614093404/http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:2003R2032:20070104:EN:PDF |date=2011-06-14}})</ref> Countries with a strong tradition of embalming corpses, such as Ireland and other colder-weather countries, have raised concerns. Despite reports to the contrary,<ref>{{cite web | first = Alkesh | last = Patel | url = http://www.webwire.com/ViewPressRel.asp?aId=41468 | title = Formaldehyde Ban set for 22 September 2007 | publisher = WebWire | date = 2007-07-04 | access-date = 2012-05-19 | archive-url = https://web.archive.org/web/20181212180926/https://www.webwire.com/ViewPressRel.asp?aId=41468 | archive-date = 2018-12-12 }}</ref> no decision on the inclusion of formaldehyde on Annex&nbsp;I of the Biocidal Products Directive for product-type&nbsp;22 (embalming and taxidermist fluids) had been made {{As of|2009|9|lc=on}}.<ref>{{cite web|url=http://esis.jrc.ec.europa.eu/ |title=European chemical Substances Information System (ESIS) entry for formaldehyde |access-date=2009-09-01 |archive-url=https://web.archive.org/web/20140101220543/http://esis.jrc.ec.europa.eu/ |archive-date=2014-01-01}}</ref>

Formaldehyde-based crosslinking is exploited in [[ChIP-on-chip]] or [[ChIP-sequencing]] genomics experiments, where DNA-binding proteins are cross-linked to their cognate binding sites on the chromosome and analyzed to determine what genes are regulated by the proteins. Formaldehyde is also used as a denaturing agent in [[RNA]] gel [[electrophoresis]], preventing RNA from forming secondary structures. A solution of 4% formaldehyde fixes pathology tissue specimens at about one mm per hour at room temperature.

====Drug testing====
Formaldehyde and 18&nbsp;[[Concentration#Molality|M]] (concentrated) [[sulfuric acid]] makes [[Marquis reagent]]—which can identify [[alkaloid]]s and other compounds.

=== Photography ===
In photography, formaldehyde is used in low concentrations for the process [[C-41 process|C-41]] (color negative film) stabilizer in the final wash step,<ref>{{cite web | url = http://www.kodak.com/global/en/service/Zmanuals/z131.shtml | title = Process C-41 Using Kodak Flexicolor Chemicals - Publication Z-131 | publisher = Kodak | access-date = 2009-09-01 | archive-url = https://web.archive.org/web/20160615095319/http://www.kodak.com/global/en/business/retailPhoto/techInfo/zManuals/z131.jhtml | archive-date = 2016-06-15 }}</ref> as well as in the [[E-6 process|process E-6]] pre-bleach step, to make it unnecessary in the final wash. Due to improvements in dye coupler chemistry, more modern (2006 or later) E-6 and C-41 films do not need formaldehyde, as their dyes are already stable.

==Safety==
In view of its widespread use, toxicity, and volatility, formaldehyde poses a significant danger to human health.<ref name= "IARC">{{citation | contribution = Formaldehyde | url = http://monographs.iarc.fr/ENG/Monographs/vol88/mono88-6.pdf | pages = 39–325 | title = Formaldehyde, 2-Butoxyethanol and 1-''tert''-Butoxypropan-2-ol | series = IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 88 | publisher = International Agency for Research on Cancer | location = Lyon, France | year = 2006 | isbn = 978-92-832-1288-1 | access-date = 2009-09-01 | archive-date = 2012-03-04 | archive-url = https://web.archive.org/web/20120304063604/http://monographs.iarc.fr/ENG/Monographs/vol88/mono88-6.pdf | url-status = live}}</ref><ref>"Formaldehyde (gas)", ''[https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/formaldehyde.pdf Report on Carcinogens, Eleventh Edition] '' (PDF), U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, 2005</ref> In 2011, the US [[National Toxicology Program]] described formaldehyde as "known to be a human carcinogen".<ref name="Harris">{{cite news | last1 = Harris | first1 = Gardiner | title = Government Says 2 Common Materials Pose Risk of Cancer | date = 2011-06-10 | url = https://www.nytimes.com/2011/06/11/health/11cancer.html | newspaper = [[The New York Times]] | access-date = 2011-06-11 | archive-url = https://web.archive.org/web/20190328042744/https://www.nytimes.com/2011/06/11/health/11cancer.html | archive-date = 2019-03-28 | url-status = live}}</ref><ref name="12Report2011">{{cite web | author = National Toxicology Program | title = 12th Report on Carcinogens | date = 2011-06-10 | publisher = [[National Toxicology Program]] | url = http://ntp.niehs.nih.gov/go/roc12 | archive-url = https://web.archive.org/web/20110608205825/https://ntp.niehs.nih.gov/index.cfm?objectid=72016262-BDB7-CEBA-FA60E922B18C2540 | archive-date = 2011-06-08 | access-date = 2011-06-11}}</ref><ref name="roc2011">{{cite web | author = National Toxicology Program | title = Report On Carcinogens - Twelfth Edition - 2011 | date = 2011-06-10 | url = https://ntp.niehs.nih.gov/go/roc12 | publisher = [[National Toxicology Program]] | access-date = 2011-06-11 | archive-url = https://web.archive.org/web/20110612085546/http://ntp.niehs.nih.gov/ntp/roc/twelfth/roc12.pdf | archive-date = 2011-06-12 }}</ref>

=== Chronic inhalation ===
{{Cleanup section|reason=A little too scattered among different types of risks. Needs some reorganization.|date=November 2023}}
Concerns are associated with chronic (long-term) exposure by inhalation as may happen from [[Thermal decomposition|thermal]] or [[chemical decomposition]] of formaldehyde-based resins and the production of formaldehyde resulting from the [[combustion]] of a variety of organic compounds (for example, exhaust gases). As formaldehyde resins are used in many [[construction materials]],<ref>{{cite journal | last1=Kristak | first1=Lubos | last2=Antov | first2=Petar | author3-link=Pavlo Bekhta | last3=Bekhta | first3=Pavlo | last4=Lubis | first4=Muhammad Adly Rahandi | last5=Iswanto | first5=Apri Heri | last6=Reh | first6=Roman | last7=Sedliacik | first7=Jan | last8=Savov | first8=Viktor | last9=Taghiyari | first9=Hamid R. | last10=Papadopoulos | first10=Antonios N. | last11=Pizzi | first11=Antonio | last12=Hejna | first12=Aleksander | title=Recent progress in ultra-low formaldehyde emitting adhesive systems and formaldehyde scavengers in wood-based panels: a review | journal=Wood Material Science & Engineering | volume=18 | issue=2 | date=2023-03-04 | issn=1748-0272 | doi=10.1080/17480272.2022.2056080 | pages=763–782 | url=https://www.tandfonline.com/doi/full/10.1080/17480272.2022.2056080 | access-date=2025-06-11| url-access=subscription }}</ref> it is one of the more common [[Indoor air quality|indoor air pollutants]].<ref>{{cite web | title= Formaldehyde in indoor air of new apartments in Greece| url=http://mantanis.users.uth.gr/S2007.pdf | access-date=2024-12-24}} by [[George Mantanis]], Eleni Vouli, Chariclea Gonitsioti and Georgios Ntalos; Presentation at the COST Action E49 Conference "Measurement and Control of VOC Emissions from Wood-Based Panels", 28-30 Nov. 2007, WKI, Braunschweig, Germany</ref><ref>{{cite web | title = Indoor Air Pollution in California | publisher = Air Resources Board, California Environmental Protection Agency | date = July 2005 | url = http://www.arb.ca.gov/research/indoor/ab1173/rpt0705.pdf | pages = 65–70 | access-date = 2012-05-19 | archive-url = https://web.archive.org/web/20190301231510/https://www.arb.ca.gov/research/indoor/ab1173/rpt0705.pdf | archive-date = 2019-03-01 }}</ref> At concentrations above 0.1&nbsp;ppm in air, formaldehyde can irritate the eyes and [[mucous membrane]]s.<ref>{{cite web | title = Formaldehyde | url = https://www.osha.gov/SLTC/formaldehyde/index.html | publisher = Occupational Safety and Health Administration | date = August 2008 | access-date = 2009-09-01 | archive-url = https://web.archive.org/web/20190411185734/https://www.osha.gov/SLTC/formaldehyde/index.html | archive-date = 2019-04-11 | url-status = live}}</ref> Formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, and can trigger or aggravate asthma symptoms.<ref>{{cite web | title = Formaldehyde Reference Exposure Levels | url = http://www.oehha.ca.gov/air/hot_spots/2008/AppendixD1_final.pdf#page=128 | publisher = California Office Of Health Hazard Assessment | date = December 2008 | access-date = 2012-05-19 | format = [[PDF]] | archive-url = https://web.archive.org/web/20190323081914/https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-technical-support-document-derivation#page=128 | archive-date = 2019-03-23 }}</ref><ref>{{cite web | title = Formaldehyde and Indoor Air | publisher = Health Canada | url = https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/air-quality/formaldehyde-indoor-air-environment-workplace-health.html | date = 2012-03-29 | archive-url = https://web.archive.org/web/20190423081005/https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/air-quality/formaldehyde-indoor-air-environment-workplace-health.html | archive-date = 2019-04-23 | access-date = 2019-04-23}}</ref>

The [[Centers for Disease Control and Prevention|CDC]] considers formaldehyde as a systemic poison. Formaldehyde poisoning can cause permanent changes in the [[nervous system]]'s functions.<ref name="cdc1">{{Cite web |title=Formaldehyde {{!}} Medical Management Guidelines {{!}} Toxic Substance Portal {{!}} ATSDR |url=https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=216&toxid=39 |access-date=2021-08-25 |publisher=Centres for Disease Control and Prevention |archive-date=2021-08-25 |archive-url=https://web.archive.org/web/20210825191526/https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=216&toxid=39 |url-status=live}}</ref>

A 1988 Canadian study of houses with [[urea-formaldehyde]] foam insulation found that formaldehyde levels as low as 0.046&nbsp;ppm were positively correlated with eye and nasal irritation.<ref>{{cite journal| last1=Broder| first1=I| last2=Corey| first2=P| last3=Brasher| first3=P| last4=Lipa| first4=M| last5=Cole| first5=P| title=Formaldehyde exposure and health status in households| pmc=1568408| year=1991| volume=95| pmid=1821362| pages=101–4| journal=Environmental Health Perspectives| doi=10.1289/ehp.9195101| bibcode=1991EnvHP..95..101B}}</ref>
A 2009 review of studies has shown a strong association between exposure to formaldehyde and the development of childhood [[asthma]].<ref>{{cite journal| last1=McGwin| first1=G| last2=Lienert| first2=J| last3=Kennedy| first3=JI| title=Formaldehyde Exposure and Asthma in Children: A Systematic Review| pages=313–7|journal=Environmental Health Perspectives| date=November 2009| issue=3| volume=118| pmid=20064771| pmc=2854756| doi=10.1289/ehp.0901143}}</ref>

A theory was proposed for the carcinogenesis of formaldehyde in 1978.<ref>{{Cite web | last = Lobachev | first = AN | title = РОЛЬ МИТОХОНДРИАЛЬНЫХ ПРОЦЕССОВ В РАЗВИТИИ И СТАРЕНИИ ОРГАНИЗМА. СТАРЕНИЕ И РАК | trans-title = Role of mitochondrial processes in the development and aging of organism. Aging and cancer | language = ru | url = http://aiexandr2010.narod.ru/rol.pdf | publisher = VINITI | year = 1978 | archive-url = https://web.archive.org/web/20130606032850/http://aiexandr2010.narod.ru/rol.pdf | archive-date = 2013-06-06 | access-date = 2012-08-01}}</ref> In 1987 the [[United States Environmental Protection Agency]] (EPA) classified it as a ''probable human carcinogen'', and after more studies the [[WHO]] [[International Agency for Research on Cancer]] (IARC) in 1995 also classified it as a ''probable human carcinogen''. Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a ''known human carcinogen''<ref name="International Agency for Research on Cancer, Monographs Vol 88">{{cite book | author = IARC Working Group on the Evaluation of Carcinogenic Risks to Humans | date = 2006 | title = IARC Monographs on the Evaluation of Carcinogenic Risks to Humans - VOLUME 88 - Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol | url = https://monographs.iarc.fr/wp-content/uploads/2018/06/mono88.pdf | publisher = WHO Press | isbn = 92-832-1288-6 | archive-url = https://web.archive.org/web/20180712054034/https://monographs.iarc.fr/wp-content/uploads/2018/06/mono88.pdf | archive-date = 2018-07-12 | access-date = 2019-04-23}}</ref> associated with nasal sinus cancer and [[nasopharyngeal cancer]].<ref name="NCI">{{cite web | date = 2011-06-10 | url = http://www.cancer.gov/cancertopics/factsheet/Risk/formaldehyde | title = Formaldehyde and Cancer Risk | publisher = National Cancer Institute | archive-url = https://web.archive.org/web/20190123172307/https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet?redirect=true | archive-date = 2019-01-23 | url-status = live}}</ref> Studies in 2009 and 2010 have also shown a positive correlation between exposure to formaldehyde and the development of [[leukemia]], particularly [[myeloid leukemia]].<ref>{{cite journal |last1=Zhang |first1=Luoping |last2=Steinmaus |first2=Craig |last3=Eastmond |first3=Eastmond |last4=Xin |first4=Xin |last5=Smith |first5=Smith |title=Formaldehyde exposure and leukemia: A new meta-analysis and potential mechanisms |url=http://ehs.sph.berkeley.edu/krsmith/CRA/cancer/ZhangL_2008.pdf |date=March–June 2009 |volume=681 |pages=150–168 |pmid=18674636 |doi=10.1016/j.mrrev.2008.07.002 |journal=[[Mutation Research (journal)|Mutation Research]] |issue=2–3 |bibcode=2009MRRMR.681..150Z |archive-url=https://web.archive.org/web/20140327073359/http://ehs.sph.berkeley.edu/krsmith/CRA/cancer/ZhangL_2008.pdf |archive-date=27 March 2014 }}</ref><ref>{{cite journal |doi=10.1002/em.20534 |pmid=19790261 |title=Formaldehyde and Leukemia: Epidemiology, Potential Mechanisms, and Implications for Risk Assessment |year=2010 |volume=51 |issue=3 |pages=181–191 |journal=Environmental and Molecular Mutagenesis |pmc=2839060 |last1=Zhang |first1=Luoping |last2=Freeman |first2=Laura E. Beane |last3=Nakamura |first3=Jun  |last4=Hecht |first4=Stephen S. |last5=Vandenberg |first5=John J. |last6=Smith |first6=Martyn T. |last7=Sonawane |first7=Babasaheb R. |bibcode=2010EnvMM..51..181Z}}</ref> Nasopharyngeal and sinonasal cancers are relatively rare, with a combined annual incidence in the United States of < 4,000 cases.<ref>{{cite web | url = https://www.cancer.org/cancer/nasopharyngeal-cancer/about/key-statistics.html | title = Key Statistics for Nasopharyngeal Cancer | publisher = American Cancer Society | access-date = 2019-04-22 | archive-url = https://web.archive.org/web/20190111232657/https://www.cancer.org/cancer/nasopharyngeal-cancer/about/key-statistics.html | archive-date = 2019-01-11 | url-status = live}}</ref><ref>{{cite journal |vauthors=Turner JH, Reh DD |title=Incidence and survival in patients with sinonasal cancer: a historical analysis of population-based data |journal=Head Neck |volume=34 |issue=6 |pages=877–85 |date=June 2012 |pmid=22127982 |doi=10.1002/hed.21830 |s2cid=205857872}}</ref> About 30,000 cases of myeloid leukemia occur in the United States each year.<ref>{{cite web | url = https://www.cancer.org/cancer/chronic-myeloid-leukemia/about/statistics.html | publisher = American Cancer Society | title = Key Statistics for Chronic Myeloid Leukemia | access-date = 2019-04-22 | archive-url = https://web.archive.org/web/20190423091903/https://www.cancer.org/cancer/chronic-myeloid-leukemia/about/statistics.html | archive-date = 2019-04-23 | url-status = live}}</ref><ref>{{cite web | url = https://www.cancer.org/cancer/acute-myeloid-leukemia/about/key-statistics.html | publisher = American Cancer Society | title = What are the key statistics about acute myeloid leukemia?Key Statistics for Acute Myeloid Leukemia (AML) | access-date = 2019-04-22 | archive-url = https://web.archive.org/web/20190423092307/https://www.cancer.org/cancer/acute-myeloid-leukemia/about/key-statistics.html | archive-date = 2019-04-23 | url-status = live}}</ref> Some evidence suggests that workplace exposure to formaldehyde contributes to sinonasal cancers.<ref name="cancer.org">{{cite web|url=http://www.cancer.org/cancer/nasopharyngealcancer/detailedguide/nasopharyngeal-cancer-risk-factors|title=Risk Factors for Nasopharyngeal Cancer|website=American Cancer Society|date=24 September 2018|access-date=17 September 2019|archive-date=10 December 2016|archive-url=https://web.archive.org/web/20161210033533/http://www.cancer.org/cancer/nasopharyngealcancer/detailedguide/nasopharyngeal-cancer-risk-factors}}</ref> Professionals exposed to formaldehyde in their occupation, such as funeral industry workers and [[Embalming|embalmers]], showed an increased risk of leukemia and brain cancer compared with the general population.<ref>{{Cite book|title = The SAGE Encyclopedia of Cancer and Society|last = Butticè|first = Claudio|publisher = SAGE Publications|year = 2015|isbn = 978-1-4833-4573-4|location = Thousand Oaks|pages = 1089–1091|editor-last = Colditz|edition = Second|chapter = Solvents|editor-first = Graham A.|doi = 10.4135/9781483345758.n530|chapter-url = https://www.academia.edu/16541375|access-date = 2015-10-27|archive-date = 2021-10-14|archive-url = https://web.archive.org/web/20211014090107/https://www.academia.edu/16541375|url-status = live}}</ref> Other factors are important in determining individual risk for the development of leukemia or nasopharyngeal cancer.<ref name="cancer.org"/><ref>{{cite web | url = https://www.cancer.org/cancer/acute-myeloid-leukemia/causes-risks-prevention/risk-factors.html | title = Risk Factors for Acute Myeloid Leukemia (AML) | publisher = American Cancer Society | date = 2018-08-21 | archive-url = https://web.archive.org/web/20190423102354/https://www.cancer.org/cancer/acute-myeloid-leukemia/causes-risks-prevention/risk-factors.html | archive-date = 2019-04-23 | url-status = live}}</ref><ref>{{cite web | url = https://www.cancer.org/cancer/chronic-myeloid-leukemia/causes-risks-prevention/risk-factors.html | title = Risk Factors for Chronic Myeloid Leukemia | publisher = American Cancer Society | date = 2018-06-19 | archive-url = https://web.archive.org/web/20181212085753/https://www.cancer.org/cancer/chronic-myeloid-leukemia/causes-risks-prevention/risk-factors.html | archive-date = 2018-12-12 | url-status = live}}</ref> In yeast, formaldehyde is found to perturb pathways for DNA repair and cell cycle.<ref>Ogbede, J. U., Giaever, G., & Nislow, C. (2021). A genome-wide portrait of pervasive drug contaminants. Scientific reports, 11(1), 12487. https://doi.org/10.1038/s41598-021-91792-1 {{Webarchive|url=https://web.archive.org/web/20211204041501/https://www.nature.com/articles/s41598-021-91792-1 |date=2021-12-04}}</ref>

In the residential environment, formaldehyde exposure comes from a number of routes; formaldehyde can be emitted by treated [[wood]] products, such as [[plywood]] or [[particle board]], but it is produced by paints, [[varnishes]], floor finishes, and [[cigarette]] smoking as well.<ref>{{cite journal |last1=Dales |first1=R |last2=Liu |first2=L |last3=Wheeler |first3=AJ |last4=Gilbert |first4=NL |title=Quality of indoor residential air and health |date=July 2008 |journal=[[Canadian Medical Association Journal]] |pmid=18625986 |volume=179 |issue=2 |pmc=2443227 |doi=10.1503/cmaj.070359 |pages=147–52}}</ref> In July 2016, the U.S. EPA released a prepublication version of its final rule on Formaldehyde Emission Standards for Composite Wood Products.<ref>{{cite web | title = Formaldehyde Emission Standards for Composite Wood Products | date = 8 July 2016 | url = https://www.epa.gov/formaldehyde/formaldehyde-emission-standards-composite-wood-products | publisher = EPA | access-date = 2019-04-24 | archive-url = https://web.archive.org/web/20181224003012/https://www.epa.gov/formaldehyde/formaldehyde-emission-standards-composite-wood-products | archive-date = 2018-12-24 | url-status = live}}</ref> These new rules impact manufacturers, importers, distributors, and retailers of products containing composite wood, including fiberboard, particleboard, and various laminated products, who must comply with more stringent record-keeping and labeling requirements.<ref>{{Cite news | url = http://www.natlawreview.com/article/epa-issues-final-rule-formaldehyde-emission-standards-composite-wood-products | title = EPA Issues Final Rule on Formaldehyde Emission Standards for Composite Wood Products | last1 = Passmore | first1 = Whitney | date = 2016-08-04 | work = The National Law Review | publisher = Womble Carlyle Sandridge & Rice, PLLC | last2 = Sullivan | first2 = Michael J. | access-date = 2016-08-24 | via = Google News | archive-url = https://web.archive.org/web/20180619070246/https://www.natlawreview.com/article/epa-issues-final-rule-formaldehyde-emission-standards-composite-wood-products | archive-date = 2018-06-19 | url-status = live}}</ref>

{{external media |width=210px |float=right |headerimage=[[File:Fema trailer 1 Mariel Carr Chemical Heritage Foundation Video.jpg|200px]] |video1=[https://www.sciencehistory.org/distillations/video/where-have-all-the-trailers-gone ''Where Have All the Trailers Gone?''], video by Mariel Carr (Videographer) &amp; Nick Shapiro (Researcher), 2015, [[Science History Institute]]}}

The U.S. EPA allows no more than 0.016&nbsp;ppm formaldehyde in the air in new buildings constructed for that agency.<ref>{{cite web|title=Testing for Indoor Air Quality, Baseline IAQ, and Materials |url=http://www.epa.gov/rtp/new-bldg/environmental/s_01445.htm |publisher=Environmental Protection Agency |archive-url=https://web.archive.org/web/20061015003607/http://www.epa.gov/rtp/new-bldg/environmental/s_01445.htm |archive-date=October 15, 2006}}</ref>{{Failed verification | date = April 2019 | reason = Dead URL & the archived document (multiple versions) doesn't show this limitation.}} A U.S. EPA study found a new home measured 0.076&nbsp;ppm when brand new and 0.045&nbsp;ppm after 30 days.<ref>M. Koontz, H. Rector, D. Cade, C. Wilkes, and L. Niang. 1996. ''Residential Indoor Air Formaldehyde Testing Program: Pilot Study.'' Report No. IE-2814, prepared by GEOMET Technologies, Inc. for the USEPA Office of Pollution Prevention and Toxics under EPA Contract No. 68-D3-0013, Washington, DC</ref> The [[Federal Emergency Management Agency]] (FEMA) has also announced limits on the formaldehyde levels in trailers purchased by that agency.<ref>{{cite news|last=Evans |first=Ben |title=FEMA limits formaldehyde in trailers |work=The Boston Globe |date=2008-04-11 |access-date=2008-09-04 |url=http://www.boston.com/news/nation/washington/articles/2008/04/11/fema_limits_formaldehyde_in_trailers/ |archive-url=https://web.archive.org/web/20100615060506/http://www.boston.com/news/nation/washington/articles/2008/04/11/fema_limits_formaldehyde_in_trailers/ |archive-date=June 15, 2010}}</ref> The EPA recommends the use of "exterior-grade" pressed-wood products with phenol instead of urea resin to limit formaldehyde exposure, since pressed-wood products containing formaldehyde resins are often a significant source of formaldehyde in homes.<ref name="NCI"/>

The eyes are most sensitive to formaldehyde exposure: The lowest level at which many people can begin to smell formaldehyde ranges between 0.05 and 1&nbsp;ppm. The maximum concentration value at the workplace is 0.3&nbsp;ppm.<ref>{{cite web | title = Formaldehyde CAS 50-00-0 | url = http://www.inchem.org/documents/sids/sids/FORMALDEHYDE.pdf | publisher = [[United Nations Environment Programme]] | access-date = 2019-04-25 | archive-url = https://web.archive.org/web/20190328010406/http://www.inchem.org/documents/sids/sids/FORMALDEHYDE.pdf | archive-date = 2019-03-28 }}</ref>{{Request quotation | date = April 2019 <!-- For the claim about the "maximum concentration in the workdplace. -->}} In controlled chamber studies, individuals begin to sense eye irritation at about 0.5&nbsp;ppm; 5 to 20 percent report eye irritation at 0.5 to 1&nbsp;ppm; and greater certainty for sensory irritation occurred at 1&nbsp;ppm and above. While some agencies have used a level as low as 0.1&nbsp;ppm as a threshold for irritation, the expert panel found that a level of 0.3&nbsp;ppm would protect against nearly all irritation. In fact, the expert panel found that a level of 1.0&nbsp;ppm would avoid eye irritation—the most sensitive endpoint—in 75–95% of all people exposed.<ref>{{cite web | author = Formaldehyde Epidemiology, Toxicology and Environmental Group, Inc | date = August 2002 | title = Formaldehyde and Facts About Health Effects | url = http://www2.dupont.com/Plastics/en_US/assets/downloads/processing/FETEG_Facts.pdf | archive-url = https://web.archive.org/web/20110511070824/http://www2.dupont.com/Plastics/en_US/assets/downloads/processing/FETEG_Facts.pdf | archive-date = 2011-05-11 }}</ref>

[[File:Rowenta Intense Pure Air air purifier.jpg|thumb|upright|Some [[air purifier]]s include filtering technology that is supposed to lower indoor formaldehyde concentration.]]

Formaldehyde levels in building environments are affected by a number of factors. These include the potency of formaldehyde-emitting products present, the ratio of the surface area of emitting materials to volume of space, environmental factors, product age, interactions with other materials, and ventilation conditions. Formaldehyde emits from a variety of construction materials, furnishings, and consumer products. The three products that emit the highest concentrations are [[medium density fiberboard]], hardwood plywood, and particle board. Environmental factors such as temperature and relative humidity can elevate levels because formaldehyde has a high [[vapor pressure]]. Formaldehyde levels from building materials are the highest when a building first opens because materials would have less time to off-gas. Formaldehyde levels decrease over time as the sources suppress.

In [[operating rooms]], formaldehyde is produced as a byproduct of electrosurgery and is present in [[surgical smoke]], exposing surgeons and healthcare workers to potentially unsafe concentrations.<ref>{{Cite journal |last1=Carroll |first1=Gregory T. |last2=Kirschman |first2=David L. |date=2023 |title=Catalytic Surgical Smoke Filtration Unit Reduces Formaldehyde Levels in a Simulated Operating Room Environment |url=https://pubs.acs.org/doi/10.1021/acs.chas.2c00071 |journal=ACS Chemical Health & Safety |language=en |volume=30 |issue=1 |pages=21–28 |doi=10.1021/acs.chas.2c00071 |s2cid=255047115 |issn=1871-5532 |access-date=2023-05-17 |archive-date=2023-05-14 |archive-url=https://web.archive.org/web/20230514040232/https://pubs.acs.org/doi/10.1021/acs.chas.2c00071 |url-status=live|url-access=subscription }}</ref>

Formaldehyde levels in air can be sampled and tested in several ways, including impinger, treated sorbent, and passive monitors.<ref>{{cite web | title = When Sampling Formaldehyde, The Medium Matters | url = http://www.galsonlabs.com/services/referenceinfo/technical_bulletins.php?tb_id=18 | publisher = Galson Labs | archive-url = https://web.archive.org/web/20110323024935/http://www.galsonlabs.com/services/referenceinfo/technical_bulletins.php?tb_id=18 | archive-date = 2011-03-23 }}</ref> The [[National Institute for Occupational Safety and Health]] (NIOSH) has measurement methods numbered 2016, 2541, 3500, and 3800.<ref>{{cite web | date = 2018-11-29 | title = NIOSH Pocket Gide to Chemical Hazards: Formaldehyde | url = https://www.cdc.gov/niosh/npg/npgd0293.html | publisher = National Institute for Occupational Safety and Health, CDC | archive-url = https://web.archive.org/web/20190328010408/https://www.cdc.gov/niosh/npg/npgd0293.html | archive-date = 2019-03-28 | url-status = live}}</ref>

In June 2011, the twelfth edition of the [[National Toxicology Program]] (NTP) Report on Carcinogens (RoC) changed the listing status of formaldehyde from "reasonably anticipated to be a human carcinogen" to "known to be a human carcinogen."<ref name="Harris" /><ref name="12Report2011" /><ref name="roc2011" /> Concurrently, a [[United States National Academy of Sciences|National Academy of Sciences]] (NAS) committee was convened and issued an independent review of the draft U.S. [[EPA IRIS]] assessment of formaldehyde, providing a comprehensive health effects assessment and quantitative estimates of human risks of adverse effects.<ref>[http://ntp.niehs.nih.gov/go/roc12 Addendum to the 12th Report on Carcinogens (PDF)] {{Webarchive|url=https://web.archive.org/web/20110608205825/https://ntp.niehs.nih.gov/index.cfm?objectid=72016262-BDB7-CEBA-FA60E922B18C2540 |date=2011-06-08}} National Toxicology Program, U.S. Department of Health and Human Services. Retrieved 06-13-2011</ref>

=== Acute irritation and allergic reaction ===
[[File:Epikutanni-test.jpg|thumb|[[Patch test]]]]

For most people, irritation from formaldehyde is temporary and reversible, although formaldehyde can cause allergies and is part of the standard patch test series. In 2005–06, it was the seventh-most-prevalent [[allergen]] in [[patch test]]s (9.0%).<ref>{{cite journal |vauthors=Zug KA, Warshaw EM, Fowler JF, Maibach HI, Belsito DL, Pratt MD, Sasseville D, Storrs FJ, Taylor JS, Mathias CG, Deleo VA, Rietschel RL, Marks J |s2cid=24088485 |title=Patch-test results of the North American Contact Dermatitis Group 2005-2006 |journal=Dermatitis |volume=20 |issue=3 |pages=149–60 |year=2009 |pmid=19470301 |doi= 10.2310/6620.2009.08097}}</ref> People with formaldehyde allergy are advised to avoid [[formaldehyde releasers]] as well (e.g., [[Quaternium-15]], [[imidazolidinyl urea]], and [[diazolidinyl urea]]).<ref>{{cite web | title = Formaldehyde allergy | url = https://www.dermnetnz.org/topics/formaldehyde-allergy/ | series = DermNet NZ | publisher = New Zealand Dermatological Society |year = 2002 | access-date = 2019-04-25 | archive-url = https://web.archive.org/web/20180923044606/https://www.dermnetnz.org/topics/formaldehyde-allergy/ | archive-date = 2018-09-23 }}</ref> People who suffer allergic reactions to formaldehyde tend to display lesions on the skin in the areas that have had direct contact with the substance, such as the neck or thighs (often due to formaldehyde released from permanent press finished clothing) or [[dermatitis]] on the face (typically from cosmetics).<ref name="Formaldehyde Releasers">{{cite journal| title=Formaldehyde-releasers: relationship to formaldehyde contact allergy. Contact allergy to formaldehyde and inventory of formaldehyde-releasers| year=2009| journal=Contact Dermatitis| volume=61| pages=63–85| doi=10.1111/j.1600-0536.2009.01582.x| last1=De Groot| first1=Anton C| last2=Flyvholm| first2=Mari-Ann| last3=Lensen| first3=Gerda| last4=Menné| first4=Torkil| last5=Coenraads| first5=Pieter-Jan| issue=2| pmid=19706047| s2cid=23404196| url=https://www.rug.nl/research/portal/en/publications/formaldehydereleasers(c3ff7adf-9f21-4564-96e0-0b9c5d025b30).html| hdl=11370/c3ff7adf-9f21-4564-96e0-0b9c5d025b30| hdl-access=free| access-date=2019-07-08| archive-date=2020-03-13| archive-url=https://web.archive.org/web/20200313130216/https://www.rug.nl/research/portal/en/publications/formaldehydereleasers(c3ff7adf-9f21-4564-96e0-0b9c5d025b30).html| url-status=live}}</ref> Formaldehyde has been banned in cosmetics in both [[Sweden]]<ref>{{Cite web |title=Formaldehyde And Formaldehyde-Releasing Preservatives |url=https://www.safecosmetics.org/chemicals/formaldehyde/ |access-date=2024-06-03 |website=Safe Cosmetics |language=en-US}}</ref> and [[Japan]].<ref>{{cite web | last1 = Hayashida | first1 = Mike | title = The Regulation of Cosmetics in Japan | url = http://www.yakujihou.com/img/CosRegulationJapan.pdf | access-date = 2019-04-25 | archive-url = https://web.archive.org/web/20190414123529/http://www.yakujihou.com/img/CosRegulationJapan.pdf | archive-date = 2019-04-14 }}</ref>

=== Other routes ===
In humans, ingestion of as little as {{Convert|30|ml|USfloz}} of 37% formaldehyde solution can cause death. Other symptoms associated with ingesting such a solution include gastrointestinal damage (vomiting, abdominal pain), and systematic damage (dizziness).<ref name="cdc1" /> Testing for formaldehyde is by blood and/or urine by [[gas chromatography–mass spectrometry]]. Other methods to detect formaldehyde include infrared detection, gas detector tubes, gas detectors using electrochemical sensors,  and [[high-performance liquid chromatography]] (HPLC). HPLC is the most sensitive.<ref>{{cite book |last=Ngwa |first=Moise |title=[[Cedar Rapids Gazette]] |date=2010-10-25 |chapter=formaldehyde testing |chapter-url=http://monographs.iarc.fr/ENG/Monographs/vol88/mono88-6A.pdf |archive-url=https://web.archive.org/web/20181025071150/https://monographs.iarc.fr/wp-content/uploads/2018/06/mono88-6A.pdf |archive-date=2018-10-25 |access-date=2012-05-19 }}</ref>

The fifteenth edition (2021) of the U.S. National Toxicology Program  Report on Carcinogens notes that currently in the U.S. "The general population can be exposed to formaldehyde primarily from breathing indoor or outdoor air, from tobacco smoke, from use of cosmetic products containing formaldehyde, and, to a more limited extent, from ingestion of food and water."  Affected water includes groundwater, surface water, and bottled water.  It also notes that occupational exposure can be significant.<ref name="auto">{{Cite report |url=https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/formaldehyde.pdf |title=RoC Profile: Formaldehyde |date=2021 |publisher=National Toxicology Program, Department of Health and Human Services}}</ref>

==Contaminant in food==
Formaldehyde in food can be present naturally, added as an inadvertent contaminant, or intentionally added as a preservative, disinfectant, or [[bacteriostatic agent]].  Cooking and smoking food can also result in formaldehyde being produced in food.  Foods that the [[U.S. National Toxicology Program]] has reported to have higher levels compared to other foods are fish, seafood, and smoked ham.  It also notes formaldehyde in food generally occurs in a bound form and that formaldehyde is unstable in an [[aqueous solution]].
<ref name="auto"/>

Scandals have broken in both the [[2005 Indonesia food scare]] and [[2007 Vietnam food scare]] regarding the addition of formaldehyde to foods to extend shelf life. In 2011, after a four-year absence, Indonesian authorities found foods with formaldehyde being sold in markets in a number of regions across the country.<ref>{{cite news | url = http://www.antaranews.com/en/news/74626/formaldehyde-laced-foods-reemerge-in-indonesian-markets | title = Formaldehyde-laced foods reemerge in Indonesian markets | date = 2011-08-10 | work = antaranews.com | archive-url = https://web.archive.org/web/20181025145949/https://en.antaranews.com/news/74626/formaldehyde-laced-foods-reemerge-in-indonesian-markets | archive-date = 2018-10-25 | url-status = live}}</ref> In August 2011, at least at two [[Carrefour]] supermarkets, the Central [[Jakarta]] Livestock and Fishery Sub-Department found [[cendol]] containing 10 [[parts per million]] of formaldehyde.<ref>{{cite news | url = http://www.thejakartaglobe.com/health/formaldehyde-tainted-rice-drinks-found-at-carrefour-markets/460829 | title = Formaldehyde-Tainted Rice Drinks Found at Carrefour Markets | work = Jakarta Globe | date = 2011-08-22 | archive-url = https://web.archive.org/web/20120928141807/http://www.thejakartaglobe.com/health/formaldehyde-tainted-rice-drinks-found-at-carrefour-markets/460829 | archive-date = 2012-09-28 }}</ref> In 2014, the owner of two noodle factories in [[Bogor]], Indonesia, was arrested for using formaldehyde in noodles.<ref>{{cite news | url = http://thejakartaglobe.beritasatu.com/news/bpom-uncovers-two-formaldehyde-tainted-noodle-factories-bogor/ | title = BPOM Uncovers Two Formaldehyde-Tainted Noodle Factories in Bogor | work = Jakarta Globe | date = 2014-10-12 | archive-url = https://web.archive.org/web/20150801225636/http://thejakartaglobe.beritasatu.com/news/bpom-uncovers-two-formaldehyde-tainted-noodle-factories-bogor/ | archive-date = 2015-08-01 }}</ref> Foods known to be contaminated included noodles, salted fish, and tofu. Chicken and beer were also rumored to be contaminated. In some places, such as China, manufacturers still use formaldehyde illegally as a preservative in foods, which exposes people to formaldehyde ingestion.<ref>
* {{cite journal | last1 = Tang | first1 = Xiaojiang | last2 = Bai | first2 = Yang | last3 = Duong | first3 = Anh | last4 = Smith | first4 = Martyn T. | last5 = Li | first5 = Laiyu | last6 = Zhang | first6 = Luoping | title = Formaldehyde in China: Production, consumption, exposure levels, and health effects | journal = Environment International | volume = 35 | issue = 8 | year = 2009 | pages = 1210–1224 | issn = 0160-4120 | doi = 10.1016/j.envint.2009.06.002| pmid = 19589601| bibcode = 2009EnInt..35.1210T }}
* see references cited on p. 1216 above
* {{cite news | title = Municipality sees red over bad blood processing | date = 2011-03-18 | url = http://www.chinadaily.com.cn/china/2011-03/18/content_12189671.htm | work = China Daily | archive-url = https://web.archive.org/web/20181024232323/http://www.chinadaily.com.cn/china/2011-03/18/content_12189671.htm | archive-date = 2018-10-24 | url-status = live}}
</ref>

In 2011 in [[Nakhon Ratchasima]], Thailand, truckloads of rotten chicken were treated with formaldehyde for sale in which "a large network", including 11 slaughterhouses run by a criminal gang, were implicated.<ref>{{cite news | title = Illegal business 'being run by a gang' | date = 2011-06-16 | url = http://www.nationmultimedia.com/2011/06/16/national/Illegal-business-being-run-by-a-gang-30157928.html | work = The Nation | archive-url = https://web.archive.org/web/20110616192558/http://www.nationmultimedia.com/2011/06/16/national/Illegal-business-being-run-by-a-gang-30157928.html | archive-date = 2011-06-16 }}</ref> In 2012, 1&nbsp;billion rupiah (almost US$100,000) of fish imported from [[Pakistan]] to [[Batam]], Indonesia, were found laced with formaldehyde.<ref>{{cite news | title = Import of formaldehyde fish from Pakistan foiled in Batam| date = 2012-02-23 | url = http://www.thejakartapost.com/news/2012/02/23/import-formaldehyde-fish-pakistan-foiled-batam.html | work = The Jakarta Post | archive-url = https://web.archive.org/web/20181216032155/https://www.thejakartapost.com/news/2012/02/23/import-formaldehyde-fish-pakistan-foiled-batam.html | archive-date = 2018-12-16 | url-status = live}}</ref>

Formalin contamination of foods has been reported in [[Bangladesh]], with stores and supermarkets selling fruits, fishes, and vegetables that have been treated with formalin to keep them fresh.<ref>{{cite news | title = Trader Fined for Selling Fish Treated with Formalin | date = 2009-08-31 | url = https://www.thedailystar.net/news-detail-103948 | work = The Daily Star | archive-url = https://web.archive.org/web/20190429100540/https://www.thedailystar.net/news-detail-103948 | archive-date = 2019-04-29 | url-status = live}}</ref> However, in 2015, a ''Formalin Control Bill'' was passed in the [[Jatiyo Sangshad|Parliament of Bangladesh]] with a provision of life-term imprisonment as the maximum punishment as well as a maximum fine of 2,000,000 [[Bangladeshi taka|BDT]] but not less than 500,000 [[Bangladeshi taka|BDT]] for importing, producing, or hoarding formalin without a license.<ref>{{cite news | title = Formalin Control Bill 2015 passed | date = 2015-02-16 | url = http://en.ntvbd.com/bangladesh/923/Formalin-Control-Bill-2015-passed | work = ntv online | archive-url = https://web.archive.org/web/20180323012557/http://en.ntvbd.com/bangladesh/923/Formalin-Control-Bill-2015-passed | archive-date = 2018-03-23 | access-date = 2015-03-04}}</ref>

In the early 1900s, formaldehyde was frequently added by US milk plants to milk bottles as a method of pasteurization due to the lack of knowledge and concern<ref>{{Cite book |last=Blum |first=Deborah |title=The poison squad: one chemist's single-minded crusade for food safety at the turn of the twentieth century |date=2018-09-25 |publisher=[[Penguin Group | Penguin Press]] |isbn=978-1-59420-514-9 |location=New York, New York |oclc=1024107182}}</ref> regarding formaldehyde's toxicity.<ref>{{cite news | title = Was Death in the Milk? | url = https://www.newspapers.com/clip/888392/formaldehyde_in_milk/ | newspaper = The Indianapolis News | date = 1900-07-31 | page = 5 | via = Newspapers.com | access-date = 2014-08-20 | archive-url = https://web.archive.org/web/20181117064648/https://www.newspapers.com/clip/888392/formaldehyde_in_milk/ | archive-date = 2018-11-17 | url-status = live}} {{Open access}}</ref><ref>{{cite news | title = Wants New Law Enacted. Food Inspector Farnsworth Would Have Use of Formaldehyde in Milk Stopped | url = https://www.newspapers.com/clip/888394/formaldehyde_in_milk/ | newspaper = The Topeka Daily Capital | date = 1903-08-30 | page = 8 | via = Newspapers.com | access-date = 2014-08-20 | archive-url = https://web.archive.org/web/20181117052444/https://www.newspapers.com/clip/888394/formaldehyde_in_milk/ | archive-date = 2018-11-17 | url-status = live}} {{Open access}}</ref>

Formaldehyde was one of the chemicals used in 19th century industrialised food production that was investigated by Dr. [[Harvey W. Wiley]] with his famous 'Poison Squad' as part of the [[US Department of Agriculture]]. This led to the 1906 [[Pure Food and Drug Act]], a landmark event in the [[early history of food regulation in the United States]].<ref>{{Cite journal |last=Meadows |first=Michelle |date=January 2006 |title=A Century of Ensuring Safe Foods and Cosmetics |url=https://www.fda.gov/media/110464/download |archive-url=https://web.archive.org/web/20210306005343/https://www.fda.gov/media/110464/download |archive-date=March 6, 2021 |journal=FDA Consumer |volume=40 |issue=1 |pages=6–13 |pmid=16528821 |format=PDF}}</ref>

== Regulation ==
Formaldehyde is banned from use in certain applications (preservatives for liquid-cooling and processing systems, [[slimicide]]s, metalworking-fluid preservatives, and antifouling products) under the Biocidal Products Directive.<ref>{{cite web |title=European Union Bans formaldehyde/formalin within Europe |publisher=European Commission's Environment Directorate-General |date=22 June 2007 |url=http://ec.europa.eu/environment/biocides/pdf/070622_withdrawal_notice.pdf |pages=1–3 |archive-url=https://web.archive.org/web/20130427152207/http://ec.europa.eu/environment/biocides/pdf/070622_withdrawal_notice.pdf |archive-date=27 April 2013 }}</ref><ref>{{cite web |title=ESIS (European Chemical Substances Information System) |publisher=European Commission Joint Research Centre Institute for Health and Consumer Protection |date=February 2009 |access-date=19 May 2012 |url=http://esis.jrc.ec.europa.eu/ |archive-url=https://web.archive.org/web/20140101220543/http://esis.jrc.ec.europa.eu/ |archive-date=1 January 2014}}</ref> In the EU, the maximum allowed concentration of formaldehyde in finished products is 0.2%, and any product that exceeds 0.05% has to include a warning that the product contains formaldehyde.<ref name="Formaldehyde Releasers"/>

In the United States, [[United States Congress|Congress]] passed a bill July 7, 2010, regarding the use of formaldehyde in hardwood [[plywood]], [[particle board]], and [[medium density fiberboard]]. The bill limited the allowable amount of formaldehyde emissions from these wood products to 0.09&nbsp;ppm, and required companies to meet this standard by January 2013.<ref>{{cite web |title=S.1660 - Formaldehyde Standards for Composite Wood Products Act |url=https://www.govtrack.us/congress/bills/111/s1660/text |date=25 August 2010 |publisher=[[GovTrack]] |archive-url=https://web.archive.org/web/20190429075804/https://www.govtrack.us/congress/bills/111/s1660/text |archive-date=29 April 2019 }}</ref> The final U.S. EPA rule specified maximum emissions of "0.05&nbsp;ppm formaldehyde for hardwood plywood, 0.09&nbsp;ppm formaldehyde for particleboard, 0.11&nbsp;ppm formaldehyde for medium-density fiberboard, and 0.13&nbsp;ppm formaldehyde for thin medium-density fiberboard."<ref>{{Cite web |title=Formaldehyde Emission Standards for Composite Wood Products |url=https://www.regulations.gov/document?D=EPA-HQ-OPPT-2016-0461-0001 |website=Regulations.gov |publisher=United States Federal Register |date=12 December 2016 |access-date=21 December 2019 |quote=The emission standards will be 0.05 ppm formaldehyde for hardwood plywood, 0.09 ppm formaldehyde for particleboard, 0.11 ppm formaldehyde for medium-density fiberboard, and 0.13 ppm formaldehyde for thin medium-density fiberboard. |archive-url=https://web.archive.org/web/20190810151643/https://www.regulations.gov/document?D=EPA-HQ-OPPT-2016-0461-0001 |archive-date=10 August 2019 }}</ref>

Formaldehyde was declared a toxic substance by the [[1999 Canadian Environmental Protection Act]].<ref>{{cite web | title = Health Canada - Proposed residential indoor air quality guidelines for formaldehyde | url = http://www.hc-sc.gc.ca/ewh-semt/pubs/air/formaldehyde/preamble-eng.php | date = April 2007 | publisher = Health Canada | archive-url = https://web.archive.org/web/20130530085603/http://www.hc-sc.gc.ca/ewh-semt/pubs/air/formaldehyde/preamble-eng.php | archive-date = 2013-05-30 }}</ref>

The [[FDA]] is proposing a ban on hair relaxers with formaldehyde due to cancer concerns.<ref>{{Cite web |title=View Rule |url=https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202304&RIN=0910-AI83 |access-date=2023-10-21 |website=www.reginfo.gov |archive-date=2023-10-20 |archive-url=https://web.archive.org/web/20231020163916/https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202304&RIN=0910-AI83 |url-status=live}}</ref>

==See also==
* [[1,3-Dioxetane]]
* [[DMDM hydantoin]]
* [[Sawdust]] | [[Health impacts of sawdust]]
* [[Sulphobes]]
* [[Transition metal complexes of aldehydes and ketones]]
* [[Wood glue]]
* [[Wood preservation]]

==References==
{{Reflist}}

==Notes==
{{reflist|group=note}}

==External links==
{{EB1911 poster|Formalin}}
* {{ICSC|0275|02}} (''gas'')
* {{ICSC|0695|06}} (''solution'')
* {{PGCH|0293}}
* {{NPI|id=45|name=Formaldehyde}}
* [http://chemsub.online.fr/name/formaldehyde.html Formaldehyde] from ChemSub Online
* [https://www.irsst.qc.ca/media/documents/pubirsst/rg-473.pdf?i=0&redirected=1 Prevention guide—Formaldehyde in the Workplace (PDF)] from the IRSST
* [https://www.cdc.gov/niosh/topics/formaldehyde/ Formaldehyde] from the [[National Institute for Occupational Safety and Health]]
* {{HSG|id=057|number=57|name=Formaldehyde|date=1991|isbn=92-4-151057-9}}
* {{EHC|89|name=Formaldehyde|date=1989|isbn=92-4-154289-6}}
* {{SIDS|id=FORMALDEHYDE|name=Formaldehyde|date=March 2002}}
* {{PPDB|359}}

{{Consumer Food Safety}}
{{Molecules detected in outer space}}
{{Transient receptor potential channel modulators}}
{{Authority control}}

[[Category:Formaldehyde| ]]