Causes

In Henoch-Schonlein purpura, some of the body's small blood vessels become inflamed, which can cause bleeding in the skin, abdomen and kidneys. It's not clear why this initial inflammation develops. It may be the result of the immune system responding inappropriately to certain triggers.

Nearly half the people who have Henoch-Schonlein purpura developed it after an upper respiratory infection, such as a cold. Other triggers include chickenpox, strep throat, measles, hepatitis, certain medications, food, insect bites and exposure to cold weather.