Comedo

Comedo
Other names: Plural: comedones[1]
Illustration comparing a normal skin pore with a whitehead and a blackhead
Specialty	Dermatology

A comedo is a clogged hair follicle (pore) in the skin.^[2][3] Keratin (skin debris) combines with oil to block the follicle.^[4] A comedo can be open (blackhead) or closed by skin (whitehead) and occur with or without acne.^[4] The word comedo comes from the Latin comedere, meaning '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.^[1]

The chronic inflammatory condition that usually includes both comedones, inflamed papules and pustules (pimples), is called acne.^[4][5] Infection causes inflammation and the development of pus.^[3] Whether a skin condition classifies as acne depends on the amount of comedones and infection.^[5] Comedones should not be confused with sebaceous filaments.

Comedo-type ductal carcinoma in situ (DCIS) is not related to the skin conditions discussed here. DCIS is a non-invasive form of breast cancer, but comedo-type DCIS may be more aggressive and so may be more likely to become invasive.^[6]

Signs and symptoms[edit | edit source]

A Comedo is small and flesh-colored with a rough texture. Furthermore are located at skin pore openings^[7]

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  Plugged follicles forming comedones

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  Open comodones

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  Multiple closed comedones at the nasolabial fold and the alar of the nose

Causes[edit | edit source]

Oil production in the sebaceous glands increases during puberty, causing comedones and acne to be common in adolescents.^[4][5] Acne is also found premenstrually and in women with polycystic ovarian syndrome.^[4] Smoking may worsen acne.^[4]

Oxidation rather than poor hygiene or dirt causes blackheads to be black.^[3] Washing or scrubbing the skin too much could make it worse, by irritating the skin.^[3] Touching and picking at comedones might cause irritation and spread infection.^[3] It is not clear what effect shaving has on the development of comedones or acne.^[3]

Some, but not all, skin products might increase comedones by blocking pores,^[3] and greasy hair products (like pomades) can worsen acne.^[4] Skin products that claim to not clog pores may be labeled noncomedogenic or non-acnegenic.^[8] Make-up and skin products that are oil-free and water-based may be less likely to cause acne.^[8] It is not known whether dietary factors or sun exposure make comedones better, worse or have no effect.^[4]

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).^[5]

Genes may play a role in the chances of developing acne.^[4] Comedones may be more common in some ethnic groups.^[4][9] People of Latino and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.^[4][9]

Pathophysiology[edit | edit source]

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.^[4] Excess keratin combined with sebum can plug the opening of the follicle.^[4][10] This small plug is called a microcomedo.^[10] Androgens increase sebum (oil) production.^[4] If sebum continues to build up behind the plug, it can enlarge and form a visible comedo.^[10]

A comedone may be open to the air ("blackhead") or closed by skin ("whitehead").^[3] Being open to the air causes oxidation, which turns it black.^[3] Cutibacterium acnes is the suspected infectious agent in acne.^[4] It can proliferate in sebum and cause inflamed pustules (pimples) characteristic of acne.^[4] Nodules are inflamed, painful deep bumps under the skin.^[4]

Comedones that are 1 mm or larger are called macrocomedones.^[11] They are closed comedones and are more frequent on the face than neck.^[12]

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.^[13]

Management[edit | edit source]

Using non-oily cleansers and mild soap may not cause as much irritation to the skin as regular soap.^[14][15] 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.^[16]

Squeezing blackheads and whiteheads can remove them, but it can also damage the skin.^[3] Doing so increases the risk of causing or transmitting infection and scarring, as well as potentially pushing any infection deeper into the skin.^[3] Comedo extractors are used with careful hygiene in beauty salons and by dermatologists, usually after using steam or warm water.^[3]

Complementary medicine options for acne in general have not been shown to be effective in trials.^[4] These include aloe vera, pyridoxine (vitamin B6), fruit-derived acids, kampo (Japanese herbal medicine), ayurvedic herbal treatments and acupuncture.^[4]

Some acne treatments target infection specifically, but there are treatments that are aimed at the formation of comedones as well.^[17] Others remove the dead layers of the skin and may help clear blocked pores.^[3][4][5]

Dermatologists can often extract open comedones with minimal skin trauma, but closed comedones are more difficult.^[4] Laser treatment for acne might reduce comedones,^[18] but dermabrasion and laser therapy have also been known to cause scarring.^[11]

Macrocomedones (1 mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light.^[11][12] The acne drug isotretinoin can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment.^[11][12]

Some research suggests that the common acne medications retinoids and azelaic acid are beneficial and do not cause increased pigmentation of the skin.^[19] If using a retinoid, sunscreen is recommended.

Rare conditions[edit | edit source]

Favre–Racouchot syndrome occurs in sun-damaged skin and includes open and closed comedones.^[20]

Nevus comedonicus or comedo nevus is a benign hamartoma (birthmark) of the pilosebaceous unit around the oil-producing gland in the skin.^[21] It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones.^[21][22]

Dowling-Degos disease is a genetic pigment disorder that includes comedo-like lesions and scars.^[23][24]

Familial dyskeratotic comedones is a rare autosomal dominant genetic condition, with keratotic (tough) papules and comedo-like lesions.^[25][26]

See also[edit | edit source]

• List of dermatology terminology

References[edit | edit source]

External links[edit | edit source]

• Rines, George Edwin, ed. (1920). "Comedones" . Encyclopedia Americana.

• What causes blackheads, Treatment and Prevention Archived 2020-01-27 at the Wayback Machine