Allergic purpura is the most common small vessel vasculitis in children. Its pathogenesis is due to the inflammatory reaction of small vessels caused by various reasons, resulting in increased permeability of the vessel wall, blood infiltration into the skin or mucous membranes and presenting as skin bruising (bruises, bruises), joint pain, abdominal pain, and in severe cases, even kidney, lung and brain involvement. Although the exact cause of the disease is not well understood, it is known that bacteria, viruses, food, drugs and chemical poisoning may be triggering factors. The majority of patients have fever, sore throat and other symptoms of upper respiratory tract infection before the onset of the disease, so it is currently believed that hemolytic streptococci and viruses are the main and important causative agents, but these factors do not act directly on the blood vessels, but cause the disease through the inflammatory reaction of the blood vessels through metaplasia, and the real allergic purpura induced by food allergy is relatively rare in clinical practice. The causes of allergic purpura: 1, bacterial and viral infections: β-hemolytic streptococcus is common among bacteria, followed by Staphylococcus aureus, Mycobacterium tuberculosis and pneumococcus. Among viruses, influenza, rubella, chickenpox, mumps and hepatitis are the most common and are the main causes of allergic purpura. 2, drugs: some drugs can also cause allergic purpura. 3, food: animal food mainly, mainly fish, shrimp, crab, milk, eggs, etc., but the real food-induced allergic purpura is relatively rare in clinical practice. 4, other: such as cold, trauma, insect bite, pollen, inoculation, tuberculin test, etc. Allergic purpura diet: In addition to avoid milk, eggs and seafood as much as possible during the acute period, as well as avoid eating indigestible coarse fiber and spicy and other excessively stimulating food to prevent gastrointestinal bleeding, generally do not have to be overly contraindicated, unless there is a clear pathogenic allergens.