View source for Comedo

{{Redirect|Blackhead}}
{{Infobox medical condition (new)
| image           = Blausen 0811 SkinPores.png
| caption         = Illustration comparing a normal skin pore with a whitehead and a blackhead
| field           = [[Dermatology]]
| synonyms        = Plural: comedones<ref name=OxfordDict />
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A '''comedo''' (plural '''comedones''') is a clogged [[hair follicle]] (pore) in the skin.<ref name=IQWiGFact>{{cite web|last=Informed Health Online|title=Acne|url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0053059/|work=Fact sheet|publisher=Institute for Quality and Efficiency in Health Care (IQWiG).|access-date=9 June 2013}}</ref> [[Keratin]] (skin debris) combines with oil to block the follicle.<ref name=LancetW/> A comedo can be open ('''blackhead''') or closed by skin ('''whitehead''') and occur with or without [[acne]].<ref name=LancetW /> The word ''comedo'' comes from [[Latin]] ''comedere'' 'to eat up' and was historically used to describe parasitic worms; in modern medical terminology, it is used to suggest the worm-like appearance of the expressed material.<ref name=OxfordDict>{{cite web|title=Comedo|url=http://oxforddictionaries.com/us/definition/american_english/comedo |archive-url=https://web.archive.org/web/20131221131750/http://www.oxforddictionaries.com/us/definition/american_english/comedo |url-status=dead |archive-date=December 21, 2013 |work=Oxford Dictionary|publisher=Oxford University Press|access-date=16 June 2013}}</ref>

The chronic inflammatory condition that usually includes comedones, inflamed papules, and pustules ([[Pimple|pimples]]) is called acne.<ref name=LancetW/><ref name=CEAcne/> Infection causes inflammation and the development of [[pus]].<ref name=IQWiGFact/> Whether a skin condition classifies as acne depends on the number of comedones and infection.<ref name=CEAcne/> Comedones should not be confused with [[sebaceous filament]]s.

Comedo-type [[ductal carcinoma in situ|ductal carcinoma ''in situ'']] (DCIS) is not related to the skin conditions discussed here. DCIS is a noninvasive form of breast cancer, but comedo-type DCIS may be more aggressive, so may be more likely to become invasive.<ref>{{cite journal|last=National Cancer Institute|title=Breast cancer treatment|url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0032676/|journal=Physician Desk Query|year=2002 |publisher=National Cancer Institute|pmid=26389187 |access-date=13 June 2013}}</ref>

==Causes==
Oil production in the [[sebaceous glands]] increases during puberty, causing comedones and [[acne]] to be common in adolescents.<ref name=LancetW /><ref name=CEAcne>{{cite journal |pmid=21477388 |pmc=3275168 |year=2011 |last1=Purdy |first1=Sarah |title=Acne vulgaris |journal=BMJ Clinical Evidence |volume=2011 |last2=De Berker |first2=David |pages=1714 }}</ref> Acne is also found premenstrually and in women with [[polycystic ovarian syndrome]].<ref name=LancetW /> Smoking may worsen acne.<ref name=LancetW /> 

[[Oxidation]] rather than poor hygiene or dirt causes blackheads to be black.<ref name=IQWiGFact/> Washing or scrubbing the skin too much could make it worse, by irritating the skin.<ref name=IQWiGFact/> Touching and picking at comedones might cause irritation and spread infection.<ref name=IQWiGFact/> What effect shaving has on the development of comedones or acne is unclear.<ref name=IQWiGFact/>

Some skin products may increase comedones by blocking pores, and greasy hair products (such as pomades) can worsen acne. Skin products that claim not to clog pores may be labeled as noncomedogenic or nonacnegenic. Makeup and skin products that are oil-free and water-based are less likely to cause acne. Whether dietary factors or sun exposure improve, worsen, or have no effect on comedones remains unknown.

A hair that does not emerge normally, an [[ingrown hair]], can also block the pore and cause a bulge or lead to infection (causing inflammation and [[pus]]).<ref name="CEAcne"/>

Genes may play a role in the chances of developing acne.<ref name=LancetW /> Comedones may be more common in some ethnic groups.<ref name=LancetW /><ref name=Davis>{{cite journal|last=Davis|first=EC|author2=Callender, VD|title=A review of acne in ethnic skin: pathogenesis, clinical manifestations, and management strategies.|journal=The Journal of Clinical and Aesthetic Dermatology|date=April 2010|volume=3|issue=4|pages=24–38|pmid=20725545|pmc=2921746}}</ref> People of [[Hispanic and Latino Americans|Latino]] and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.<ref name=LancetW /><ref name=Davis />

==Pathophysiology==
[[File:Comedos Nose 01.jpg|thumb|Multiple open comedones at the [[nasolabial fold]] and the alar of the nose]]
Comedones are associated with the [[pilosebaceous unit]], which includes a [[hair follicle]] and [[sebaceous gland]]. These units are mostly on the face, neck, upper chest, shoulders, and back.<ref name=LancetW /> Excess keratin combined with [[sebum]] can plug the opening of the follicle.<ref name=LancetW /><ref name=Burkhart>{{cite journal|last=Burkhart|first=CG|author2=Burkhart, CN|title=Expanding the microcomedone theory and acne therapeutics: Propionibacterium acnes biofilm produces biological glue that holds corneocytes together to form plug.|journal=Journal of the American Academy of Dermatology|date=October 2007|volume=57|issue=4|pages=722–4|pmid=17870436|doi=10.1016/j.jaad.2007.05.013}}</ref> This small plug is called a microcomedo.<ref name="Burkhart"/>  [[Androgens]] increase sebum (oil) production.<ref name=LancetW>{{cite journal|last=Williams|first=HC|author2=Dellavalle, RP |author3=Garner, S |title=Acne vulgaris.|journal=Lancet|date=Jan 28, 2012|volume=379|issue=9813|pages=361–72|pmid=21880356|doi=10.1016/S0140-6736(11)60321-8|s2cid=205962004}}</ref> If sebum continues to build up behind the plug, it can enlarge and form a visible comedo.<ref name="Burkhart"/>

A comedo may be open to the air ("blackhead") or closed by skin ("whitehead").<ref name=IQWiGFact/> Being open to the air causes oxidation of the melanin pigment, which turns it black.<ref>{{Cite book |title=Robbins & Cotran Pathologic Basis of Disease |date=2021 |publisher=Elsevier |isbn=978-0-323-53113-9 |editor-last=Kumar |editor-first=Vinay |edition=10th |location=Philadelphia, PA |pages=1165 |editor-last2=Abbas |editor-first2=Abul K. |editor-last3=Aster |editor-first3=Jon C. |editor-last4=Turner |editor-first4=Jerrold R. |editor-last5=Perkins |editor-first5=James A. |editor-last6=Robbins |editor-first6=Stanley L. |editor-last7=Cotran |editor-first7=Ramzi S.}}</ref><ref name=IQWiGFact/> ''[[Cutibacterium acnes]]'' is the suspected infectious agent in acne.<ref name=LancetW /> It can proliferate in sebum and cause inflamed [[pustules]] (pimples) characteristic of acne.<ref name=LancetW /> [[Nodule (medicine)|Nodules]] are inflamed, painful, deep bumps under the skin.<ref name=LancetW />

Comedones that are 1&nbsp;mm or larger are called macrocomedones.<ref name=Pearl>{{cite journal|last=Wise|first=EM|author2=Graber, EM|title=Clinical pearl: comedone extraction for persistent macrocomedones while on isotretinoin therapy.|journal=The Journal of Clinical and Aesthetic Dermatology|date=November 2011|volume=4|issue=11|pages=20–1|pmid=22132254|pmc=3225139}}</ref> They are closed comedones and are more frequent on the face than neck.<ref name=PCDS>{{cite web|last=Primary Care Dermatology Society|title=Acne: macrocomedones|url=http://www.pcds.org.uk/clinical-guidance/macrocomedones|work=Clinical Guidance|publisher=Primary Care Dermatology Society|access-date=12 June 2013}}</ref>

Solar comedones (sometimes called senile comedones) are related to many years of exposure to the sun, usually on the cheeks, not to acne-related pathophysiology.<ref>{{cite web|last=DermNetNZ|title=Solar comedones|url=http://www.dermnetnz.org/reactions/solar-comedones.html|publisher=New Zealand Dermatological Society|access-date=16 June 2013}}</ref>

==Management==
Using nonoily cleansers and mild soap may not cause as much irritation to the skin as regular soap.<ref>{{cite journal|last=Poli|first=F|title=[Cosmetic treatments and acne].|journal=La Revue du Praticien|date=Apr 15, 2002|volume=52|issue=8|pages=859–62|pmid=12053795}}</ref><ref>{{cite journal|last=Korting|first=HC|author2=Ponce-Pöschl, E |author3=Klövekorn, W |author4=Schmötzer, G |author5=Arens-Corell, M |author6= Braun-Falco, O |title=The influence of the regular use of a soap or an acidic syndet bar on pre-acne.|journal=Infection|date=Mar–Apr 1995|volume=23|issue=2|pages=89–93|pmid=7622270|doi=10.1007/bf01833872|s2cid=39430391}}</ref> Blackheads can be removed across an area with commercially available [[pore strips|pore-cleansing strips]] (which can still damage the skin by leaving the pores wide open and ripping excess skin) or the more aggressive [[cyanoacrylate]] method used by dermatologists.<ref name=Pagnoni>{{cite journal|last=Pagnoni|first=A|author2=Kligman, AM |author3=Stoudemayer, T |title=Extraction of follicular horny impactions the face by polymers. Efficacy and safety of a cosmetic pore-cleansing strip (Bioré)|journal=Journal of Dermatological Treatment|year=1999|volume=10|issue=1|pages=47–52|doi=10.3109/09546639909055910}}</ref>

Squeezing blackheads and whiteheads can remove them, but  can also damage the skin.<ref name=IQWiGFact/> Doing so increases the risk of causing or transmitting infection and scarring, as well as potentially pushing any infection deeper into the skin.<ref name=IQWiGFact/> Comedo extractors are used with careful hygiene in beauty salons and by dermatologists, usually after using steam or warm water.<ref name=IQWiGFact />

[[Complementary medicine]] options for acne in general have not been shown to be effective in trials.<ref name=LancetW /> These include aloe vera, [[pyridoxine]] (vitamin B<sub>6</sub>), fruit-derived acids, [[kampo]] (Japanese herbal medicine), [[ayurvedic]] herbal treatments, and acupuncture.<ref name=LancetW />

Some [[Acne#Management|acne treatments]] target infection specifically, but some treatments are aimed at the formation of comedones, as well.<ref name=Gollnick>{{cite journal|last=Gollnick|first=HP|author2=Krautheim, A|title=Topical treatment in acne: current status and future aspects.|journal=Dermatology|year=2003|volume=206|issue=1|pages=29–36|pmid=12566803|doi=10.1159/000067820|s2cid=11179291}}</ref> Others remove the dead layers of the skin and may help clear blocked pores.<ref name=IQWiGFact/><ref name=LancetW/><ref name="CEAcne"/>

[[Dermatologists]] can often extract open comedones with minimal skin trauma, but closed comedones are more difficult.<ref name=LancetW /> Laser treatment for acne might reduce comedones,<ref>{{cite journal|last=Orringer|first=JS|author2=Kang, S |author3=Hamilton, T |author4=Schumacher, W |author5=Cho, S |author6=Hammerberg, C |author7=Fisher, GJ |author8=Karimipour, DJ |author9=Johnson, TM |author10= Voorhees, JJ |title=Treatment of acne vulgaris with a pulsed dye laser: a randomized controlled trial|journal=JAMA: The Journal of the American Medical Association|date=Jun 16, 2004|volume=291|issue=23|pages=2834–9|pmid=15199033|doi=10.1001/jama.291.23.2834|doi-access=}}</ref> but dermabrasion and laser therapy have also been known to cause scarring.<ref name="Pearl"/>

Macrocomedones (1&nbsp;mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light.<ref name="Pearl"/><ref name="PCDS"/> The acne drug [[isotretinoin]] can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment.<ref name="Pearl"/><ref name="PCDS"/>

Some research suggests that the common acne medications [[retinoid]]s and [[azelaic acid]] are beneficial and do not cause increased pigmentation of the skin.<ref name=Woolery-Lloyd>{{cite journal|last=Woolery-Lloyd|first=HC|author2=Keri, J |author3=Doig, S |title=Retinoids and azelaic Acid to treat acne and hyperpigmentation in skin of color.|url= https://jddonline.com/articles/dermatology/S1545961613P0434X |journal=[[Journal of Drugs in Dermatology]]|date=Apr 1, 2013|volume=12|issue=4|pages=434–7|pmid=23652891}} {{free access}} </ref> If using a retinoid, sunscreen is recommended.

==Rare conditions==
[[Favre–Racouchot syndrome]] occurs in sun-damaged skin and includes open and closed comedones.<ref name="Bolognia">{{cite book |author1=Rapini, Ronald P. |author2=Bolognia, Jean L. |author3=Jorizzo, Joseph L. |title=Dermatology: 2-Volume Set |publisher=Mosby |location=St. Louis |year=2007 |pages=1847 |isbn=978-1-4160-2999-1 }}</ref>

''[[Nevus comedonicus]]'' or comedo nevus is a benign [[hamartoma]] (birthmark) of the [[pilosebaceous unit]] around the oil-producing gland in the skin.<ref name=Zarkik>{{cite journal |last=Zarkik |first=S |author2=Bouhllab, J |author3=Methqal, A |author4=Afifi, Y |author5=Senouci, K |author6= Hassam, B |title=''Keratoacanthoma arising in nevus comedonicus''. |journal=Dermatology Online Journal |date=Jul 15, 2012 |volume=18 |issue=7 |pages=4 |doi=10.5070/D38XZ7951S |pmid=22863626}}</ref> It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones.<ref name="Zarkik"/><ref>{{cite web |last=DermNetNZ |title=Comedo Naevus |url=http://www.dermnetnz.org/lesions/comedone-naevus.html |publisher=New Zealand Dermatological Society |access-date=16 June 2013}}</ref>

[[Dowling–Degos disease]] is a genetic pigment disorder that includes comedo-like [[lesions]] and scars.<ref>{{cite journal |last=Bhagwat |first=PV |author2=Tophakhane, RS |author3=Shashikumar, BM |author4=Noronha, TM |author5= Naidu, V |title=Three cases of Dowling Degos disease in two families. |journal=Indian Journal of Dermatology, Venereology and Leprology |date=Jul–Aug 2009 |volume=75 |issue=4 |pages=398–400 |pmid=19584468 |doi=10.4103/0378-6323.53139 |url=https://tspace.library.utoronto.ca/bitstream/1807/48445/1/dv09126.pdf|doi-access=free}}</ref><ref>{{cite journal |last=Khaddar |first=RK |author2=Mahjoub, WK |author3=Zaraa, I |author4=Sassi, MB |author5=Osman, AB |author6=Debbiche, AC |author7= Mokni, M |title=[Extensive Dowling-Degos disease following long term PUVA therapy]. |journal=Annales de Dermatologie et de Vénéréologie |date=January 2012 |volume=139 |issue=1 |pages=54–7 |pmid=22225744 |doi=10.1016/j.annder.2011.10.403}}</ref>

Familial dyskeratotic comedones are a rare [[Dominance (genetics)|autosomal-dominant]] genetic condition, with keratotic (tough) papules and comedo-like lesions.<ref name=Hallermann>{{cite journal |last=Hallermann |first=C |author2=Bertsch, HP |title=Two sisters with familial dyskeratotic comedones. |journal=European Journal of Dermatology |date=Jul–Aug 2004 |volume=14 |issue=4 |pages=214–5 |pmid=15319152}}</ref><ref>{{cite web |last=OMIM |title=Comedones, familial dyskeratotic |url=http://cadd.whu.edu.cn/ditad/diseaseOMIMList/?page=879 |work=OMIM database |publisher=OMIM |access-date=13 June 2013 |url-status=dead |archive-url=https://archive.today/20130615093140/http://cadd.whu.edu.cn/ditad/diseaseOMIMList/?page=879 |archive-date=15 June 2013}}</ref>

==References==
{{reflist|2}}

== External links ==
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* {{Cite Americana|wstitle=Comedones}}
*[https://www.health-exp.com/2020/01/what-Causes-Blackheads.html What causes blackheads, Treatment and Prevention] {{Webarchive|url=https://web.archive.org/web/20200127081714/https://www.health-exp.com/2020/01/what-Causes-Blackheads.html |date=2020-01-27 }}
{{Disorders of skin appendages}}
[[Category:Dermatologic terminology]]
[[Category:Acneiform eruptions]]
[[Category:Puberty]]
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