This is a picture of diffuse, cutaneous mastocytosis. Abnormal collections of cells in the skin (mast cells) produce this rash. Unlike bullous mastocytosis, rubbing will not lead to formation of blisters (bullae).
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.