Acne occurs when glands (called sebaceous glands) in the follicles of the skin become overactive. These glands produce sebum, an oily substance that helps to stop the skin drying out. Someone with acne produces too much sebum, which forms a plug with dead skin cells and blocks the follicle.
Sebaceous glands produce a substance called sebum, which is responsible for keeping the skin and hair moisturized. During adolescence, sebaceous glands enlarge and produce more sebum under the influence of hormones, also called androgens. After about age 20, sebum production begins to decrease.
Sebum produced by the sebaceous gland combines with cells being sloughed off within the hair follicle and “fills up” the hair follicle. When the follicle is “full,” the sebum spreads over the skin surface, giving it an oily appearance. When this process works correctly, the skin is moisturized and remains healthy.
The bacteria Propionibacterium acnes, often shortened to P. acnes, normally resides in the pores. It uses sebum as a nutrient for growth. As sebum production increases, the number of P. acnes bacteria increases in the pore. In the microcomedone stage, the bacteria do not cause infection because they are only in the material inside the pore, not infecting the skin.