Blackhead Health Dictionary

A semi-solid, black-capped plug of greasy material, also known as a comedo, blocking the outlet of a sebaceous (oil-forming) gland in the skin. Blackheads occur most commonly on the face, chest, shoulders, and back and are associated with increased sebaceous gland activity. They are one of the features of most types of acne.

n. a plug formed of fatty material (sebum and keratin) in the outlet of a *sebaceous gland in the skin; the black colour is due to *melanin. See also acne. Medical name: comedo.