A bruise, also called a contusion, is a type of relatively minor hematoma of tissue in which capillaries and sometimes venules are damaged by trauma, allowing blood to seep into the surrounding interstitial tissues. Bruises can involve capillaries at the level of skin, subcutaneous tissue, muscle, or bone. A bruise may be named by the length of its diameter as an petechia (less than 3 mm), purpura (3 mm to 1 cm) or ecchymosis (1 to 3 cm), although these terms can also refer to internal bleeding not caused by trauma.