A
comedo is a clogged
hair follicle (pore) in the skin.
Keratin (skin debris) combines with oil to block the follicle. A comedo can be open (
blackhead) or closed by skin (
whitehead), and occur with or without
acne. The word comedo comes from
Latin to suggest the worm-like look of a blackhead that has been secreted. The plural of comedo is
comedones.