A halo nevus occurs when the body develops an immune response to the pigment cells around a nevus. The pigment disappears and the area becomes white. Often in the process, the nevus itself disappears, leaving a circular white spot (macula).
Update Date 7/30/2014
Updated by: Richard J. Moskowitz, MD, Dermatologist in private practice, Mineola, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.