Henoch-Schönlein is caused by an abnormal response of the immune system. The result is inflammation in the microscopic blood vessels in the skin. Blood vessels in the joints, kidneys, or the intestines may also be affected. It is unclear why this occurs.
The syndrome is mostly seen in children, but it may affect people of any age. It is more common in boys than in girls. Many people who develop this disease had an upper respiratory infection in the weeks before.
Gordon A. Starkebaum, MD, Professor of Medicine, Division of Rheumatology, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.