A bruise, medically termed a contusion, is localized subcutaneous hemorrhage resulting from blunt trauma to the skin and underlying tissues. The mechanism involves the rupture of small capillaries and venules within the dermis and hypodermis, allowing blood to leak into the surrounding interstitial space. The visible discoloration is caused by the pooling of blood and subsequent breakdown of hemoglobin. Over days, the body initiates a complex process of resorption, transforming the initial red-purple color through various stages—such as green and yellow—as the blood components are metabolized and reabsorbed by the circulatory and lymphatic systems.