I’ve heard the same old rumors (as I’m sure many others have) since the early 1990’s, some insisting Jackson had his skin somehow lightened, either chemically or medically. Others explain that he had a skin condition known as vitiligo, which turns skin lighter through depigmentation. People counter that argument by saying there has never been a documented case of vitiligo causing depigmentation as widespread as Jackson’s. I’ve yet to see either argument backed by compelling data, and to the best of my knowledge, this debate continues informally to this day, along with whether or not Elvis is still alive and whether or not Paul McCartney is an impostor.
From Skeptics - Stack Exchange
More about vitilgo than I ever wanted to know.