Allergic purpura, also known as hedgehog purpura, is an IgA antibody-mediated hypersensitivity reaction capillary and small vessel vasculitis, basically characterized by non-thrombocytopenic skin purpura, accompanied by joint pain, abdominal pain and kidney damage. The causes of allergic purpura are complex. Infection with bacteria (e.g. Streptococcus haemolyticus), viruses (e.g. influenza virus) and intestinal parasites can cause the disease; food (fish, shrimp, eggs, etc.) xenoproteins, pollen, dust mites, etc. can cause allergic reactions leading to the disease; some drugs such as salicylates, antibiotics, barbiturates, sulfonamides, isoniazid, etc. can cause the disease. The mechanism of the disease is type III allergic reaction, when the antigen and antibody (mainly IgA) combine, circulating immune complexes can be formed and deposited in the blood vessel wall, and complement can be activated, which leads to inflammation in the capillary and small blood vessel wall and its surrounding tissues, and increases the permeability of the blood vessel wall, resulting in various clinical manifestations. Elevated levels of IgA-type antibodies can lead to increased deposition of IgA immune complexes in the skin and kidneys, thus causing the disease. Sometimes there are also cellular immune abnormalities, and the role of genetic immunity in the pathogenesis may also be present. For the prevention and treatment of allergic purpura, we should try to avoid upper respiratory infection, avoid taking suspicious drugs and food, etc.