Comedo / Comedones
A comedo (comedones for plural) is a sebaceous follicle (also known as a pore) that is plugged with a matter made up of dead skin cells and small hair cells from within the follicle, known as sebum. Open comedones are often called blackheads because they oxidize and create a dark discoloration. Closed comedones are sometimes referred to as whiteheads since they do not discolor, but still contain sebum.
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