Purpura generally belongs to hemorrhagic diseases and belongs to hematology, but if it is allergic purpura, it can also belong to dermatology. 1. Clinical purpura is divided into allergic purpura and thrombocytopenic purpura. Thrombocytopenic purpura is mainly caused by platelet disorders, which is mainly manifested by bleeding of the skin and mucous membranes, so you should choose hematology when you visit the doctor. 2. If the platelet count is normal and there is no abnormality in the coagulation function, it is considered that it may be allergic purpura, which is a kind of allergic vasculitis that infringes on the capillaries and small blood vessels of the skin or other organs, and it is necessary to pay attention to finding allergic allergens and keeping away from the allergens by examination, and it is necessary to choose the Department of Dermatology in the consultation. The specific situation needs to go to the hospital for examination to determine, in order to prevent delay.