What is vitiligo or white patches on the body and what causes it?

There are treatments for vitiligo that are at least partly effective in many cases, but its cause is still under study.

A prominent theory is that an autoimmune reaction is involved. The condition may also be associated with certain ailments, including thyroid disorders, and may flare up after injury, stress, or severe sunburn.

Patches occur in all races when pigment cells in the skin, called melanocytes, are destroyed and can no longer produce the pigment melanin.

The most common treatment involves a drug called psoralen, taken orally. When followed by exposure to natural sunlight or ultraviolet light, the drug seems to make pigment cells migrate from hair follicles to white areas.

In some patients, steroids stop the spread of pigment loss. In others, such as the singer Michael Jackson, doctors use chemicals to lighten unaffected skin areas so they blend in with those where pigment has been lost.

Medical authorities also recommend avoiding excessive exposure to the sun. Tanning darkens normal areas, which makes the light patches more prominent because they do not tan.