Bruising on the surface of the body caused by a minor bump may be due to bleeding of the skin and mucous membranes caused by the body’s hemostatic or coagulation dysfunction. Bleeding of the skin and mucous membranes is usually generalized or limited to the skin and mucous membranes spontaneously or difficult to stop bleeding after the injury. Blood pools under the skin or mucous membranes, forming red or dark red spots that do not fade when pressed. There are three main causes: 1. Abnormalities in the function of the blood vessel wall, commonly seen in hereditary hemorrhagic capillary dilatation, allergic purpura, severe infections and vitamin C deficiency. 2. Platelet abnormalities, such as thrombocytopenic idiopathic thrombocytopenic purpura, platelet apoplexy, and so on. 3. Coagulation abnormalities, such as hemophilia, coagulation factor deficiency, hyperfibrinolysis, hypofibrinogenemia, severe liver disease and other diseases. The causes of skin and mucous membrane bleeding are numerous and the mechanisms are complex, so it is recommended to look for the causes and take treatment measures under the professional guidance of hematologists. At the same time, avoid trauma, bumping to avoid bleeding occurs.