Urticaria pigmentosa is characterized by few to many brownish spots which itch and, when scratched, produce welts and reddened skin. The brown spots contain cells with high levels of histamine. Individuals sometimes develop flushing and headache resulting from the massive release of histamine from these spots. This is the typical appearance of one of these spots (often referred to as a mastocytoma).
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.