Comedo

Oil production in the sebaceous glands increases during puberty, causing comedones and acne to be common in adolescents.{{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 }} Acne is also found premenstrually and in women with polycystic ovarian syndrome. Smoking may worsen acne.

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

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).

Genes may play a role in the chances of developing acne. Comedones may be more common in some ethnic groups.{{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}} People of Latino and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.

File:Comedos Nose 01.jpg 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. Excess keratin combined with sebum can plug the opening of the follicle.{{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}} This small plug is called a microcomedo. Androgens increase sebum (oil) production.{{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}} If sebum continues to build up behind the plug, it can enlarge and form a visible comedo.

A comedo may be open to the air ("blackhead") or closed by skin ("whitehead"). Being open to the air causes oxidation of the melanin pigment, which turns it black.{{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.}} Cutibacterium acnes is the suspected infectious agent in acne. It can proliferate in sebum and cause inflamed pustules (pimples) characteristic of acne. Nodules are inflamed, painful, deep bumps under the skin.

Comedones that are 1 mm or larger are called macrocomedones.{{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}} They are closed comedones and are more frequent on the face than neck.{{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}}

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.{{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}}

Using nonoily cleansers and mild soap may not cause as much irritation to the skin as regular soap.{{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}}{{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}} Blackheads can be removed across an area with commercially available 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.{{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}}

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

Complementary medicine options for acne in general have not been shown to be effective in trials. These include aloe vera, pyridoxine (vitamin B₆), fruit-derived acids, kampo (Japanese herbal medicine), ayurvedic herbal treatments, and acupuncture.

Some acne treatments target infection specifically, but some treatments are aimed at the formation of comedones, as well.{{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}} Others remove the dead layers of the skin and may help clear blocked pores.

Dermatologists can often extract open comedones with minimal skin trauma, but closed comedones are more difficult. Laser treatment for acne might reduce comedones,{{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=}} but dermabrasion and laser therapy have also been known to cause scarring.

Macrocomedones (1 mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light. The acne drug isotretinoin can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment.

Some research suggests that the common acne medications retinoids and azelaic acid are beneficial and do not cause increased pigmentation of the skin.{{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}} If using a retinoid, sunscreen is recommended.

Favre–Racouchot syndrome occurs in sun-damaged skin and includes open and closed comedones.{{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 }}

Nevus comedonicus or comedo nevus is a benign hamartoma (birthmark) of the pilosebaceous unit around the oil-producing gland in the skin.{{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}} It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones.{{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}}

Dowling–Degos disease is a genetic pigment disorder that includes comedo-like lesions and scars.{{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}}{{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}}

Familial dyskeratotic comedones are a rare autosomal-dominant genetic condition, with keratotic (tough) papules and comedo-like lesions.{{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}}{{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}}

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