[3] A comedo can be open (blackhead) or closed by skin (whitehead) and occur with or without acne.

[3] 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.

[1] The chronic inflammatory condition that usually includes comedones, inflamed papules, and pustules (pimples) is called acne.

Comedo-type ductal carcinoma in situ (DCIS) is not related to the skin conditions discussed here.

[5] Oil production in the sebaceous glands increases during puberty, causing comedones and acne to be common in adolescents.

[3] Skin products that claim to not clog pores may be labeled noncomedogenic or nonacnegenic.

[3][7] Comedones are associated with the pilosebaceous unit, which includes a hair follicle and sebaceous gland.

[2] Comedo extractors are used with careful hygiene in beauty salons and by dermatologists, usually after using steam or warm water.

[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] Some research suggests that the common acne medications retinoids and azelaic acid are beneficial and do not cause increased pigmentation of the skin.

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

[22][23] Familial dyskeratotic comedones are a rare autosomal-dominant genetic condition, with keratotic (tough) papules and comedo-like lesions.