While acne affects the majority of teenagers, it can also appear later in life. Acne is so common that it can almost be considered a normal part of growing up. Indeed, acne is the most common skin disease in the U.S. Understanding how your skin functions is important in understanding acne. Acne is a disease of the skin's sebaceous glands and hair follicles. The job of the sebaceous glands is to secrete an oil called sebum that lubricates the skin and keeps it soft and pliable.
Sebaceous glands are largest and most numerous on the face and in areas where acne tends to strike.
The sebum produced by these glands empties into the skin's hair follicles, tiny canals which cover most of the body. Sebum ultimately reaches the surface of the skin by passing through the hair follicle. Every follicle on the body has a hair, although the hair may be so fine that it is nearly invisible. Pore size seems to be a family trait, like eye color. The outer layer of skin around the opening of the hair follicle also plays an important role in acne.