Purple patches on the skin of elderly people, generally called petechiae or petechiae, the causes can be divided into three aspects: 1, thrombocytopenic purpura, the causes are excessive platelet destruction, impaired generation, ineffective generation, divided into three conditions: 1, idiopathic thrombocytopenic purpura, refers to the body produces platelet autoantibodies, resulting in increased platelet destruction, mostly autoimmune causes. 2, secondary thrombocytopenic purpura, mostly for vitamin B12 deficiency, folic acid deficiency, severe infection, bone marrow blood related diseases, splenomegaly. 3, thrombotic thrombocytopenic purpura, mostly caused by decreased ability of microvascular endothelial cells to resist thrombosis and excessive platelet consumption. Thrombocytopenic purpura is mainly a significant reduction of platelets, which may be accompanied by severe visceral bleeding and intracranial hemorrhage in addition to the appearance of skin petechiae. Second, allergic purpura, it refers to the invasion of fine arteries, capillary allergic vasculitis, related to autoimmunity, mostly seen in children, in addition to skin purpura, may also be accompanied by abdominal pain, joint pain, hematuria, proteinuria, etc. Third, elderly people take more antithrombotic drugs, such as aspirin, and are prone to skin petechiae.