I am in my 20s, and I still have to deal with acne. Why? I thought I would be through with it by this time. What can I do for it?

The teen years are the peak years for having acne, but some adults have to struggle with it too. During adolescence, 85 percent of youngsters have it to some degree. Most are rid of it by age 25. However, 12 percent of women and 3 percent of men have to contend with it until their 40s, and a few, even later. In fact, some adults get acne for the first time later in life.

Acne is caused by the plugging of skin follicles -- ''pores,'' as many call them. Oil sludge and shed skin cells form the plug. Every skin follicle comes equipped with an oil gland. Even when the follicle opening is plugged, the gland keeps secreting oil downstream of the plug. The follicle swells and eventually bursts, spewing oil into the adjacent skin. A pimple forms.

One reason why adolescence is the peak age for acne has to do with male hormones. They make their appearance then, and their production is in high gear. Male hormones (females make them too) stimulate oil production. In addition to distending follicles, oil is a favorite meal for some skin bacteria that live in the follicle. Those bacteria multiply and add to the inflammation of the oil spill. Hormone production continues in adult years, and that's one reason why adults are still subject to acne.

Treatment of all acne involves unplugging the follicle and getting rid of the skin bacteria that contribute to it. Benzoyl peroxide and salicylic acid are ingredients found in many over-the-counter acne preparations, and they can unplug clogged follicles. If they produce no results, creams, lotions and gels with ingredients related to vitamin A promote follicle drainage. Retin-A, Renova, Differin and Tazorac are examples. The next step, if needed, is antibiotic creams and gels that come to the rescue. The last step on the ladder is vitamin A-related oral medicines.