Allergic purpura is a syndrome of leukocyte fragmentation vasculitis involving capillaries and small arteries caused by various allergens. The clinical manifestations are non-thrombocytopenic purpura with or without joint damage, spasmodic abdominal colic, gastrointestinal bleeding and renal lesions. It occurs in children and adolescents, generally more in males than females, and is more common in spring and autumn. Most cases have a history of upper respiratory tract infection 1 to 3 weeks prior to the onset of the disease. The onset of the disease is rapid, with skin purpura as the first manifestation, but may also involve the kidneys, joints, gastrointestinal tract, cardiovascular and nervous system. It is a very important and important part of the disease. 1, skin type purpura Also known as simple purpura, that is, only skin palpable purpura. The typical skin rash is symmetrical and occurs on the buttocks and extremities, especially on the extensor side of both lower extremities, with mostly sparse pinpoint to soybean-sized petechiae or petechiae, but also erythema, maculopapular rash, blistering or pemphigoid damage, or even blood blisters, necrosis, and ulcers. The rash often appears in batches. Purpura usually turns brown gradually in 1 to 2 weeks and fades without leaving traces. It can also be prolonged for weeks or months. 2, arthritic purpura for non-wandering multi-joint involvement, more common, the incidence of about 50%. Most of them occur after purpura, with pain and swelling in knee, ankle, elbow, wrist and other joints, which do not cause joint deformity and can recur. 3, gastrointestinal purpura Also known as abdominal purpura, common in children, 90% of children appear in the course of the disease, about 50% of adults occur. It is characterized by sudden onset of spasmodic abdominal pain with mild pressure pain and no rebound pain or muscle tension. It mostly follows the rash and worsens as the rash increases. The abdominal pain is not fixed, often located around the umbilicus, but can also radiate to other parts of the abdomen, often accompanied by nausea, vomiting, diarrhea and mucus stool, and in severe cases, vomiting blood, blood in the stool, intestinal entrapment and intestinal obstruction and other signs of acute abdomen, occasionally intestinal perforation. 4, renal purpura Usually 20-60% of patients with renal damage 4-8 weeks after purpura. It is characterized by microscopic or visual hematuria, proteinuria, hypertension, edema and renal insufficiency, which can last for 1-6 weeks, or it can recur and become chronic. 5.Mixed purpura is accompanied by 2 or more of the above 3 types in addition to the simple skin type.