Purple rash(Purpura) over your lower legs, and buttocks. It can also appear on your arms, torso, face.
The joints in your knees and ankles can become swollen and arthritic ridden
In about eight days of having the rash many of the younger children have abdominal pain, nausea, vomiting, or bloody stools.
Most cases of H.S.P. involve some sort of Kidney disease because the kidneys manifest itself as a protein or blood in your urine
In some rare cases there have been seizures, and pneumonia
Causes
HSP is caused when an abnormal immune system response, when your body starts to attack its own cells and organs, specifically the blood vessels. There is no known reason for this response of your immune system, but most cases of HSP come after a respiratory tract infection, HIV, hepatitis, chickenpox, measles. It can also be triggered by some different foods that your body has an abnormal response to, some medications, or even trauma.
Complications
Having HSP you do have a risk of having perminent kidney damage, or even kidney faliure, but that only happens in about 1% of children and 40% of adults (within 15 years of being diagnosed). Another complication is intussusception of the bowel, which means a section of your large or small intestine folds over itself, blocking the bowel. Women who have had HSP have a higher risk of high blood pressure and proteinuria while pregnant.