Bruising is considered to be caused by rupture of subcutaneous blood vessels, coagulation dysfunction, platelet abnormality and other factors. 1. Rupture of subcutaneous blood vessels: when bumping, the local skin will be damaged by external force, resulting in the rupture of subcutaneous capillaries and the formation of bruises, accompanied by pressure and pain, and if the amount of bleeding is more, a hematoma can be formed. 2. Coagulation dysfunction: If the patient suffers from hemophilia, vitamin K deficiency and other diseases, or long-term, large doses of anticoagulants, such as warfarin, aspirin and other drugs, can affect the coagulation function, resulting in systemic bleeding tendency and difficulty in hemostasis, so the patient is prone to bruising after the bump. 3. Platelet abnormality: If you suffer from leukemia, aplastic anemia and other diseases, the number of platelets can be significantly reduced or functional defects, leading to spontaneous bleeding, resulting in bruises after bumping. If there are no other discomforts associated with the bruise, the patient can observe the bruise for a period of time. If there are other discomforts, such as difficulty in stopping bleeding, extensive and serious bruising of skin and mucous membrane, the patient should go to the hospital immediately to find out the cause of the disease and receive treatment as soon as possible.