Michael Jackson startled one of television's largest audiences ever two weeks ago when he told Oprah Winfrey that he does not bleach his skin, as many had suspected. Instead, he said, he has "a skin disorder. "His dermatologist identified it as vitiligo, an often unsightly but noncontagious condition that causes skin to lose its pigmentation. PEOPLE asked Dr. James J. Nordlund, 53, a dermatologist who is director of the Pigment Clinic at the University of Cincinnati Medical Center, to tell us more about the surprisingly common disease.

How many people in the U.S. are affected by vitiligo?

The best estimate is slightly less than one in every 100 persons—somewhere between 1 and 2 million people with varying degrees of severity—affecting blacks and whites equally.

What does vitiligo do to skin?

The disease destroys pigment cells, which comprise about 5 percent of the epidermis, in a patch) distribution. It leaves the skin more susceptible to sunburn and damage from injuries.

What is its impact on patients?

It's not biologically life-threatening, but it certainly can destroy a life. Imagine looking in the mirror and having white blotches all over your face, your hands, your neck, your genitalia. About a third of our patients really are depressed from it.

Does everyone who has a tiny patch of white on their body have the disease?

No. Vitiligo is one of hundreds of disorders—from mild fungus infections to lupus—that can produce white spots.

How does Vitiligo show-itself?

Usually you notice white blotches around the eyes or on the cheek and chin or the backs of the hands or knees. Then new spots can appear. In some people it can spread so rapidly that they can be totally depigmented in six months. Often it starts in childhood; 50 percent gel it before the age of 20 and 95 percent before 40.

How do you treat the disease?

The standard treatment for people with a relatively little amount of vitiligo is to apply a mild cortisone cream once a day for three to six months. For extensive cases, patients take a drug called psoralen and are exposed to long-wave ultraviolet light twice a week for three to 12 months. Up to 70 percent of our patients get a significant amount of pigment back. If the condition is too extensive—where patients are 70 to 80 percent depigmented—we take the remaining pigment out using a cream called Benoquin. But we always try to gel the pigment back first.