There are many reasons for bruising, the most common reason is trauma, such as local violent stimulation, collision, etc., which causes bruising will repair itself and can be treated without treatment, or you can use hot water to apply hot compresses every day to promote the absorption of bruising. It may also be due to the aging of human blood vessels, mostly seen in the elderly, bruising can occur after a slight collision, and there are very few blood diseases, such as thrombocytopenia or coagulation disorders, bruising does not need any reason to appear on its own. If the bruises appear repeatedly on the body, it is best to go to the hospital in time to check, if it is not a blood disease, do not worry, they can slowly recover, if it is a blood disease need to be treated early.