Allergic purpura: It is a systemic vasculitis syndrome with small vasculitis as the main pathological change. It is characterized by a combination of skin purpura, joint pain, abdominal pain, blood in stool, hematuria and proteinuria. The disease is self-limiting, usually healing in 3-6 weeks, but is prone to recurrence, and the greatest danger is the complication of nephritis, even to renal failure. The cause and pathogenesis of allergic purpura is not completely clear, it may be related to the following factors: a. Infections include: bacteria, viruses, parasites. Bacterial infections are commonly β-hemolytic streptococcus, Staphylococcus aureus, Mycobacterium tuberculosis, Mycobacterium typhi, Pneumococcus and Pseudomonas, etc. The above respiratory infections are common, as well as pneumonia, tonsillitis, scarlet fever, bacterial dysentery, urinary tract infections, impetigo, tuberculosis and local infections (skin, teeth, mouth, middle ear). Viral infections such as rubella, influenza, measles, chicken pox, mumps, hepatitis, etc. are common. Parasitic infections such as roundworm infections, hookworm, whipworm, tapeworm, schistosome, trichomonas vaginalis and plasmodium infections are also common. Second, food factors mainly include: milk, eggs, fish, shrimp, crab, clams and other allergic protein allergy. Third, there are drugs: antibiotics, sulfonamides, antipyretic and analgesic agents. Such as chloramphenicol, streptomycin, isoniazid, aminopyrine, aspirin, sulfonamides and other drugs may cause allergic purpura. Fourth, in addition, cold, trauma, mental factors, pollen, mosquito bites, vaccination can also cause allergic purpura.