Who is affected by Henoch-Schonlein purpura (HSP)?

Henoch-Schonlein purpura is an immune disease causing small hemorrhages in the skin and may also be associated with kidney damage. It is the most common acute vasculitis ("blood vessel inflammation") affecting children, with an incidence of approximately 10 cases per 100,000 children per year. Although the syndrome is usually seen in children, people of any age may be affected. It is more common in boys than in girls. The cause is unknown and may be the result of a viral infection or reaction to medication.