What are comedones?
Comedones form when follicles become blocked by a mixture of sebum (oil) and dead skin cells (see the Understanding Acne page for more details). The blockage traps sebum inside the follicle and allows Proprionobacterium acnes (P. acnes) bacteria to grow. If the follicle is open to the outside air, the melanin (skin pigment) in the dead skin cells oxidizes and becomes dark in color, forming a blackhead. If the follicle remains closed, a whitehead forms. Inflammation of the follicle can occur, producing papules and pustules.
