Why do we bruise?

Bruises - because the body has received a heavy blow which injures the bodily tissues without rupturing or tearing the outer covering of skin. A bruise is a wound, and a wound may be defined as a breach in the continuity of any body tissue. Often the skin is cut or torn. But closed wounds, such as the rupturing of internal organs, may leave no visible external sign. A bruise, or contusion of the skin, is caused by the rupture of the blood vessels in the deeper layers of the tissues under the skin. The blood escapes from the damaged vessels into the surrounding tissues and brings about discoloration of the skin, which at first goes red, and then "black and blue". As the blood pigments break down, the bruise changes to yellow and green, and eventually fade away. Usually bruises show in the area where the blow has fallen. But there times when the blood will track along muscles and the planes of connective tissue, causing the bruise to appear some way away from the injury.