Allergic purpura is a non-thrombocytopenic small-vessel vasculitis that invades the skin and the fine arteries and capillaries of other organs. Infection, allergy (food, drugs), and insect bites are possible triggers, and type III allergic reaction is its main pathogenesis. The disease occurs mostly in preschool children, with a high incidence in autumn and winter, and a history of whistling tract infection before the onset. Allergic purpura involves not only the skin, but also the joint muscular system, digestive system, and urinary system. It is also called simple purpura when there is only skin damage; it is also called abdominal purpura when there is abdominal pain, diarrhea, blood in stool and other gastrointestinal manifestations; it is called renal purpura when there is renal damage such as hematuria and proteinuria; it is called arthritic purpura when there is joint and muscle swelling and pain, and it is called mixed type when 2 or more systems are involved. Clinical manifestations: 1, skin: repeatedly appearing petechiae, petechiae of different sizes, pressure does not fade, that is purpura, purpura can be fused into a patch, serious cases can occur wind-like edema, blisters, blood blisters, necrosis and even ulcers. It usually fades within 1 to 2 weeks and leaves no trace. The rash mostly occurs in weight-bearing areas, preferably on the extensor side of the limbs, with relatively symmetrical distribution and appearing in batches. 2, digestive system: abdominal pain, pressure pain, usually around the navel, may be accompanied by nausea, vomiting, some have blood stool, a few children can be complicated by intussusception, intestinal obstruction, intestinal perforation, intestinal necrosis, etc.. 3.Urological system: manifesting as hematuria under the eyes or microscopic hematuria, proteinuria, tubular urine. Urinary symptoms may appear with the rash or after the rash subsides, and in severe cases, chronic nephritis, nephrotic syndrome and renal failure may occur. Renal involvement is the main factor determining the chronic course of the disease and mortality. 4, joint muscle system: manifested as joint muscle swelling, pain, may be accompanied by limited movement. The most commonly affected joints are the knee and ankle joints, but the wrist, elbow and fingers can also be involved. The joint lesions are mostly transient and do not leave joint deformity after fading. Treatment: 1. Etiological treatment: actively search and treat the possible causes. If there is an infection induced by the need for anti-infection treatment. 2. General treatment: Those with severe rash or swollen joints and muscles in the acute stage should rest in bed. Those with gastrointestinal symptoms should abstain from water, apply antispasmodic drugs for abdominal pain; use antipyretic and analgesic drugs for fever and joint pain; apply drugs to improve vascular fragility (such as rutin, vitamin C, calcium, etc.), antihistamine drugs (such as loratadine, levocetirizine, etc.). 3.Anti-platelet agglutination drugs: aspirin, dipyridamole, etc. 4.Adrenocorticotropic hormone: suitable for severe skin damage or joint type, abdominal type, renal type purpura. 5.Immunosuppressants: such as cyclophosphamide, mainly used for renal damage that cannot be controlled by the application of glucocorticoids. 6.Severe cases can be treated with high-dose gammaglobulin shock therapy or plasma replacement.