Most of us get a few blackheads or pimples now and then. These small bumps or blemishes on the skin are quite normal. They soon go away and are nothing to worry about. The skin problem called acne can be more troubling, though. It's a long-lasting, sometimes severe flareup of pimples, most often on the face, chest, and back.

Acne erupts when a hair follicle-the tube in which a hair grows-becomes plugged with dead skin cells and a natural oil called sebum that helps moisten and protect the skin. The follicle swells and the skin around it may become red and tender. It may also become infected with bacteria.

Acne is the most common skin problem in the United States. Anyone of any age can get it, even infants, but it's most common in teenagers. Up to 85 percent of all teens have acne. About one adult in five gets acne now and then.

Many people believe that greasy foods or chocolates cause acne, but in fact they're not the problem. If you have acne, you can put most of the blame on your hormones: They affect how much sebum your skin's oil glands make. Acne tends to peak during the teen years because that's when hormones, and oil glands, are most active.

Acne is most often harmless, though it can be annoying, and some people who have acne may feel shy or self-conscious around others. Minor bouts clear up by themselves after a week or two. Sometimes, though, severe acne leaves scars. There is no sure way to prevent acne, but you can do a lot to treat it and keep it from getting worse.