It is common to see bruising on the arm after blood is drawn. The syringe needle is inserted into the vein through the epidermis, dermis and subcutaneous tissues during the blood draw, and a small amount of blood will flow into the subcutaneous tissues during the extraction of the syringe needle, which will accumulate in the subcutaneous tissues and form a bruise. With mild pain, the pain increases after pressure, mainly due to the formation of vascular wounds and bruises stimulating the surrounding tissue, do not worry too much. You can use chilled mineral water to apply cold compresses for about 10 minutes to prevent the blood from continuing to pool, and use hot towels to apply hot compresses at two-hour intervals to accelerate local blood circulation, so that the bruises can be absorbed faster and the skin can recover faster to achieve the purpose of treatment.