While it typically occurs when the immune system does not function as it should, the precise cause of allergic purpura is unknown, explains KidsHealth. However, some cases have had links to typhoid, cholera, yellow fever, measles and hepatitis B vaccinations and various foods, drugs, chemicals and insect bites, notes WebMD.
Allergic purpura, also known as Henoch-Schonlein purpura, may also have links with the cooler temperatures of fall and winter, reports WebMD. The disorder occurs significantly more often in children than adults, and typically between the ages of 2 and 11, according to KidsHealth. Classic symptoms include rash, joint pain and swelling, abdominal pain, and blood in the urine, explains WebMD.