Henoch-Schönlein purpura (HSP) is a vasculitis (inflammation of blood vessels) that affects small blood vessels mainly in the skin, intestines, and kidneys. Symptoms can begin in children, most commonly between the ages of 4 and 7 years, soon after an upper respiratory tract infection or a streptococcalpharyngitis (sore throat infection). Children may develop arthritis (inflammation of the joints), leading to pain. A rash may start as hive-like spots (urticaria) or small raised red spots (erythematous maculopapules) on the legs and buttocks. Eventually these spots blend to form bigger areas of bruising (purpura) in the skin. Children may also develop abdominal pain that can be quite severe. Children younger than 2 years with HSP are more likely to develop edema (swelling of various areas of their bodies), which is a result of leaky small blood vessels in the skin. Kidney involvement can also cause edema, hematuria (visible or microscopic blood in the urine), or proteinuria (protein in the urine).