Bruising on the arm is a common symptom in clinical practice, and the main reasons include the following: 1. It may be caused by unintentional bump or squeeze on the arm, which may cause subcutaneous bruising, and the bruising will be absorbed gradually within ten or 24 hours, and sometimes the area is relatively large. Some bruises on the arm may be caused by non-traumatic factors, such as capillary fragility or vitamin C deficiency, as well as hematologic diseases, including hemophilia and coagulation factor deficiency, which may result in poor formation of coagulation mechanisms and easy rupture of small blood vessels on the skin surface, resulting in arm bruises. phenomenon. It is necessary to go to a regular hospital for detailed examination to find the real cause of the disease and to carry out systematic and standardized treatment according to the cause.