Comedo

Oil production in the sebaceous glands increases during puberty, causing comedones and acne to be common in adolescents.^[3][4] Acne is also found premenstrually and in women with polycystic ovarian syndrome.^[3] Smoking may worsen acne.^[3]

Oxidation rather than poor hygiene or dirt causes blackheads to be black.^[2] Washing or scrubbing the skin too much could make it worse, by irritating the skin.^[2] Touching and picking at comedones might cause irritation and spread infection.^[2] What effect shaving has on the development of comedones or acne is unclear.^[2]

Some skin products might increase comedones by blocking pores,^[2] and greasy hair products (such as pomades) can worsen acne.^[3] Skin products that claim to not clog pores may be labeled noncomedogenic or nonacnegenic.^[6] Make-up and skin products that are oil-free and water-based may be less likely to cause acne.^[6] Whether dietary factors or sun exposure make comedones better, worse, or neither is unknown.^[3]

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).^[4]

Genes may play a role in the chances of developing acne.^[3] Comedones may be more common in some ethnic groups.^[3][7] People of Latino and recent African descent may experience more inflammation in comedones, more comedonal acne, and earlier onset of inflammation.^[3][7]

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.^[3] Excess keratin combined with sebum can plug the opening of the follicle.^[3][8] This small plug is called a microcomedo.^[8] Androgens increase sebum (oil) production.^[3] If sebum continues to build up behind the plug, it can enlarge and form a visible comedo.^[8]

A comedo may be open to the air ("blackhead") or closed by skin ("whitehead").^[2] Being open to the air causes oxidation of the melanin pigment, which turns it black.^[9][2] Cutibacterium acnes is the suspected infectious agent in acne.^[3] It can proliferate in sebum and cause inflamed pustules (pimples) characteristic of acne.^[3] Nodules are inflamed, painful, deep bumps under the skin.^[3]

Comedones that are 1 mm or larger are called macrocomedones.^[10] They are closed comedones and are more frequent on the face than neck.^[11]

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.^[12]

Using nonoily cleansers and mild soap may not cause as much irritation to the skin as regular soap.^[13][14] 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.^[15]

Squeezing blackheads and whiteheads can remove them, but can also damage the skin.^[2] Doing so increases the risk of causing or transmitting infection and scarring, as well as potentially pushing any infection deeper into the skin.^[2] Comedo extractors are used with careful hygiene in beauty salons and by dermatologists, usually after using steam or warm water.^[2]

Complementary medicine options for acne in general have not been shown to be effective in trials.^[3] These include aloe vera, pyridoxine (vitamin B₆), fruit-derived acids, kampo (Japanese herbal medicine), ayurvedic herbal treatments, and acupuncture.^[3]

Some acne treatments target infection specifically, but some treatments are aimed at the formation of comedones, as well.^[16] Others remove the dead layers of the skin and may help clear blocked pores.^[2][3][4]

Dermatologists can often extract open comedones with minimal skin trauma, but closed comedones are more difficult.^[3] Laser treatment for acne might reduce comedones,^[17] but dermabrasion and laser therapy have also been known to cause scarring.^[10]

Macrocomedones (1 mm or larger) can be removed by a dermatologist using surgical instruments or cauterized with a device that uses light.^[10][11] The acne drug isotretinoin can cause severe flare-ups of macrocomedones, so dermatologists recommend removal before starting the drug and during treatment.^[10][11]

Some research suggests that the common acne medications retinoids and azelaic acid are beneficial and do not cause increased pigmentation of the skin.^[18] If using a retinoid, sunscreen is recommended.

Favre–Racouchot syndrome occurs in sun-damaged skin and includes open and closed comedones.^[19]

Nevus comedonicus or comedo nevus is a benign hamartoma (birthmark) of the pilosebaceous unit around the oil-producing gland in the skin.^[20] It has widened open hair follicles with dark keratin plugs that resemble comedones, but they are not actually comedones.^[20][21]

Dowling–Degos disease is a genetic pigment disorder that includes comedo-like lesions and scars.^[22][23]

Familial dyskeratotic comedones are a rare autosomal-dominant genetic condition, with keratotic (tough) papules and comedo-like lesions.^[24][25]

• Rines, George Edwin, ed. (1920). "Comedones" . Encyclopedia Americana.
• What causes blackheads, Treatment and Prevention Archived 2020-01-27 at the Wayback Machine