What causes a bruise?

Bruises are caused by injuries to the body that result in damage to the small blood vessels under the skin's surface. These blood vessels rupture and release blood into the surrounding tissue, causing discoloration and swelling. The blood usually settles and becomes visible at or just below the skin's surface. As the body reabsorbs the blood within the bruise, its colors change due to chemical reactions between the blood cells and proteins in the tissue. Over time, a fresh bruise goes from the common bluish-purple hue and gradually progresses through colors from dark green to light yellow before disappearing as healing completes.