Sebaceous glands produce a substance called sebum which is responsible for keeping the skin and hair moisturized. Sebum is a light yellow, oily fluid.
During adolescence, sebaceous glands enlarge and produce more sebum under the influence of hormones 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 the skin an oily appearance. When this process works correctly, the skin is moisturized and remains healthy.
If not enough sebum is produced, the skin is dry. On the other hand, if too much sebum is produced the skin is oily, a condition called seborrhea. If sebum gets trapped in the pores, acne can develop.
