Allergic purpura definition: Allergic purpura, is a systemic vasculitis with small vasculitis as the main lesion, clinical features are platelet non-decreasing purpura, can be accompanied by joint swelling and pain, abdominal pain, blood in stool, hematuria, etc., mostly occurs in children from 2 to 8 years old, slightly more boys than girls, the onset of all seasons of the year, traditionally believed to be more in spring and autumn, personally believe that the onset of slightly more when turning season. Clinical manifestations: ① skin purpura: recurrent skin purpura, mostly on the extremities and buttocks, symmetrical distribution, appearing in batches, initially purplish red, slightly above the skin plane, suppressed without fading, partially fused; ② gastrointestinal symptoms: seen in about 2/3 of cases, intestinal wall edema, hemorrhage, necrosis or intestinal perforation is the main cause, may appear paroxysmal abdominal pain, accompanied by vomiting, may appear black stool or bloody stool, occasionally see intestinal overlap, intestinal obstruction; ③ joint (3) Joint symptoms: 1/3 of the cases may have swollen and painful joints such as knee, ankle, elbow and wrist joints with restricted activities, which usually disappear after a few days; (4) Renal symptoms: if the kidneys are involved, the symptoms vary in severity, such as hematuria, proteinuria and tubular urine, etc. Pay attention to the review of routine urine examination; (5) Other manifestations: severe cases may have intracranial hemorrhage, myocarditis, pericarditis, laryngeal edema, pulmonary hemorrhage, etc.