Atopic vasculitis is an autoimmune disorder that causes small blood vessels in the skin, joints, intestines, and kidneys to become inflamed and bleed. The condition is most common in children ages 2 to 6.

Allergic vasculitis is an autoimmune disease of unknown cause, with widespread damage to the microvascular system in many organs, mainly involving the skin, kidneys, intestines and joints. The disease occurs at all ages but often occurs in children and young people.