The four main characteristics of Henoch-Schonlein purpura include: 
Rash (purpura). Reddish-purple spots that look like bruises develop on the buttocks, legs and feet. The rash can also appear on the arms, face and trunk and may be worse in areas of pressure, such as the sock line and waistline.
Swollen, sore joints (arthritis). People with Henoch-Schonlein purpura often have pain and swelling around the joints — mainly in the knees and ankles. Joint pain sometimes precedes the classical rash by one or two weeks. These symptoms subside when the disease clears and leave no lasting damage.
Digestive tract symptoms. Many children with Henoch-Schonlein purpura develop belly pain, nausea, vomiting and bloody stools. These symptoms sometimes occur before the rash appears.
Kidney involvement. Henoch-Schonlein purpura can also affect the kidneys. In most cases, this shows up as protein or blood in the urine, which you may not even know is there unless you have a urine test done. Usually this goes away once the illness passes, but some people develop persistent kidney disease.
