1, allergic people should pay special attention. Allergic purpura is a common type of bleeding disorder in school-age children. Most of the children themselves are allergic, and under the action of certain external allergenic substances, the body undergoes a metamorphic (allergic) reaction, causing widespread small-vessel vasculitis, leading to increased small-vessel fragility and permeability, exudative purpura and edema. 2. Infections and drugs may be the cause of sensitization. The pathogenesis of the disease is not fully understood, and is currently believed to be related to an autoimmune reaction mediated by an immunoglobulin called IgA in the human body. The disease is caused by various bacterial, viral and parasitic infections, such as colds, tonsillitis, measles, chicken pox, rubella and intestinal roundworm disease; consumption of foods rich in animal protein such as fish, shrimp, crab, eggs and milk, stimulating foods such as chili, wine and raw garlic; and the use of antibiotics (such as penicillin, streptomycin, chloramphenicol, cephalosporins, etc.), antipyretic and analgesic agents (salicylates, pau d’arco, etc.), tranquilizers Sulfonamides, atropine, etc., can be causative factors. In addition, some children are prone to allergic purpura when they are exposed to pollen, dust, cold, mosquito bites, or after vaccination. 3, the disease can be mild or serious. The disease has obvious seasonality, generally more in winter and spring, less in summer. Most of the children will have general discomfort, low fever, malaise, and upper respiratory tract infection and other prodromal symptoms 1~2 weeks before the onset of the disease, followed by the emergence of skin purpura, which is mostly seen on the lower limbs, around the ankle joints and buttocks. The typical rash is often a 3-5 mm subcutaneous bleeding spot, above the skin surface, like chicken skin, and does not fade when pressed. The rash usually subsides within 1-2 weeks, but can recur and be prolonged for weeks or even months, but does not leave a trace after it subsides. Many children also develop abdominal pain, often paroxysmal colic, mostly around the umbilicus, which occurs at the same time as the rash or within a week. In some cases, swelling, pain, and pressure in the joints (mostly in the large joints of the knee, ankle, wrist, elbow, etc.) and difficulty moving can last for several days. A few develop optic nerve atrophy, iritis, retinal hemorrhage and edema, and central nervous system-related symptoms such as convulsions. Nearly half of the children develop purpura nephritis with varying degrees of renal damage 2 to 4 weeks after the skin purpura disappears. The children may be asymptomatic and only show microscopic hematuria or proteinuria in the urine routine, or they may also have carnivorous hematuria. The earlier the appearance of urinary abnormalities, the more severe the manifestation of nephritis. Most of the kidney damage can be clinically self-healing, but some will recur, evolving into chronic nephritis, nephrotic syndrome, and even renal failure, the prognosis is poor. 4, self-limiting disease, no preventive prescription. The disease is currently mainly symptomatic and supportive treatment, including bed rest during the acute period, the use of appropriate antibiotics for infected people, to avoid and remove allergic factors. For those who only have skin purpura symptoms, compound lutin, calcium, vitamin C and antihistamine preparations are available; for fever and arthritis symptoms, corticosteroids are available; for recurrent and severe purpura nephritis, immunosuppressive drugs can be added. The disease is a self-limiting disease, most of the children have a good prognosis, but some can relapse after a few weeks or months, so you must follow the doctor’s instructions and review the disease on time.