Allergic purpura is a vasculitis syndrome with small vasculitis as the main lesion. The clinical manifestation is a characteristic rash, often accompanied by arthralgia, joint effusion, abdominal pain, blood in the stool and proteinuria and hematuria. It occurs most frequently in preschool and school-age children. The incidence is higher in boys than in girls. There is often a history of upper respiratory tract infection 1-3 weeks before the onset of the disease; it may be accompanied by systemic symptoms such as low-grade fever, poor nasal function and fatigue; the first symptoms are mostly skin purpura; some cases first appear abdominal pain, arthritis or kidney symptoms. 1, skin purpura: the repeated appearance of skin purpura during the course of the disease is the characteristic of the disease. It is mostly found on the limbs and buttocks, symmetrically distributed, more on the extensor side, in batches, and less on the face and trunk, initially as purplish papules, higher than the skin surface, and then brownish. In severe cases, purpura may fuse into large blisters with hemorrhagic necrosis. It is accompanied by urticaria and angioneurotic edema. Gastrointestinal symptoms: More than half of the children have recurrent paroxysmal abdominal pain, located around the umbilicus or lower abdomen; it may be accompanied by vomiting, but vomiting blood is rare; some children have black or bloody stools, diarrhea or constipation; occasionally, intestinal overlap, intestinal obstruction or intestinal perforation. 3. Joint symptoms: painful swelling of large joints such as knee, ankle, elbow, wrist, etc., occurring singly or repeatedly, with restricted movement; there is often fluid in the joint cavity, and joint symptoms disappear quickly; they may also disappear within a few months, leaving no sequelae. 4, renal symptoms: renal lesions are seen in 30%-60% of children, often appear within 1-8 weeks of the disease, symptoms vary in severity, most children appear hematuria, proteinuria and tubular, accompanied by increased blood pressure and swelling, a small number of nephrotic syndrome performance, occasionally acute renal failure; most of them can be completely recovered; about 6% of children develop chronic nephritis, uremia. 5, other manifestations: Occasionally, intracranial hemorrhage may occur, resulting in convulsions, paralysis, coma, aphasia, and also nosebleeds, gum bleeding, hemoptysis, testicular bleeding, etc.