A halo nevus is a lesion with a centrally placed nevus surrounded by a white halo of depigmented (loss of pigment) skin. It is most commonly seen in adolescence, but can be observed at any age. Over a period of months to years, the halo nevus gradually involutes and disappears, often leaving a residual white patch.
The trigger or cause of spontaneous pigment loss in a halo nevus is not known; however, pigment loss is the result of an immunologic process in which melanocytes are destroyed (pigment-producing cells). In essence, the body’s immune cells attack other cells of the body.
This relatively common disorder occurs between the first and fifth decades of life, most frequently during late adolescence. Halo nevi can occur almost anywhere on the body, but most often appear on the trunk, especially the back. As many as 50 percent of affected individuals have more than one halo nevus.
The phenomenon seems to follow several stages. The first is a sudden appearance of the white halo around the mole. In the following months or years the central nevus disappears. Finally, the white patch may re-pigment spontaneously and return to normal skin color. However, the white area often remains.