A contusion, commonly known as a bruise, is a type of hematoma of tissue in which capillaries and sometimes venules are damaged by trauma, allowing blood to seep, hemorrhage, or extravasate into the surrounding interstitial tissues. Most bruises are not very deep under the skin so that the bleeding causes a visible discoloration. The bruise then remains visible until the blood is either absorbed by tissues or cleared by immune system action. Bruises, which do not blanch under pressure, can involve capillaries at the level of skin, subcutaneous tissue, muscle, or bone. Bruises are not to be confused with other similar-looking lesions primarily distinguished by their diameter or causation. These lesions include petechia, purpura, and ecchymosis.