Lynn Marie Jenes, age 15, of Davenport, Iowa, for her question:

WHAT CAUSES ACNE?

Acne is a skin problem that is chiefly a disorder of adolescence and is related to the hormonal changes of this time of life. It starts with the thickening and drying of the sebum, the otherwise oily secretion of the sebaceous glands. Acne most often appears on the face, neck and back.

A plug, called a blackhead, forms in the gland opening or follicle. This stops the normal flow of sebum and often results in swelling or pimples.

Other complications can develop. Lumps and bacterial infections may set in and cysts may form. Acne is very common, often hitting 80 to 90 percent of all teen agers.

Most acne seems to be caused by conditions in the body's internal chemistry, and many times the disease continues until it has run its course    which often continues until the patient passes into adulthood. But doctors have good luck also with diet, since some certain foods seem to aggravate the condition. Skin cleanliness is also important in treating acne.