Bruises are areas of skin discoloration that occur due to damage to small blood vessels and blood entering the surrounding tissues. Most often, they appear after a blow, compression, or other mechanical injury without violation of the integrity of the skin.
During the healing process, the color of the bruise can gradually change from reddish or blue-purple to greenish and yellow. Most bruises go away on their own, but their frequent appearance for no apparent reason, significant size, or concomitant bleeding may be grounds for seeing a doctor.