Bruising is also known as subcutaneous bleeding, and in most cases is caused by external injuries. Most of the bruises caused by external injury factors will fade slowly and there are no obvious adverse symptoms. In case of bruising, cold compresses should be applied within 24 hours and never hot compresses. If the bruise does not disappear, it may be related to platelet abnormalities, kidney lesions, abnormal blood vessel wall function, lack of blood nutrients, and excessive toxins in the blood. For bruising caused by these adverse factors, professional testing must be done. In these diseases, bruising is only an external symptom, if the primary disease is not effectively solved. Then there is no way to recover from the bruise.