Henoch–Schönlein purpura (HSP) causes irritation and swelling (inflammation) of the small blood vessels, which can result in a prominent skin rash, arthritis (inflammation of the joints), abdominal pain and nephritis (inflammation of the blood vessels within the kidney). It is one of the more common types of vasculitis (inflamed blood vessels) in children. Your doctor will measure your child’s blood pressure regularly and check for signs of kidney inflammation, such as blood or protein in the urine. Depending on how serious the condition is, your child may need a kidney biopsy and treatment with medication to calm the immune system. Long-term kidney disease (called glomerulonephritis) develops in about 5% of children with HSP. HSP mostly affects children ages 2 to 10, but it can also affect older children and teens. Early treatment can help prevent long-term damage to the kidneys.