What Causes Blackheads?
A comedo is a clogged hair follicle or pore. If the pore is open and filled with oil and dead skin cell debris, it turns gray or black giving it the name "blackhead." A blackhead's dark color is not due to trapped dirt (so you can’t wash it away) but from a buildup of melanin pigment in the pore that is oxidized (think of how metal turns rusty and dark when exposed to oxygen). Ironically, a blackhead can also be yellowish if the pigment does not become oxidized.
Blackheads appear as one of the first signs of puberty from the overproduction of oil that occurs with the surge of androgen hormones. Because blackheads are caused by oil trapped inside the pore, adults with oily skin are likely to have them as well. Blackheads usually localize in the "T-Zone" of the face (forehead, nose, and chin) but may also appear on the back, chest, arms and shoulders, wherever there is a great density of hair follicles with their attached oil glands.
The use of some topical face oils and makeup can cause blackheads to form. A product that won't clog your pores, or create comedones is called "noncomedogenic", so look for this term on a label.