Why do bruises turn yellow, purple, and green? — Sophie Langdon, New York, New York
Michael Omori, director of the Pediatric Emergency Center at St. Vincent Mercy Medical Center in Toledo, Ohio, answers:
Bruises usually result from trauma to muscle or other tissues just below the skin. The trauma ruptures tiny blood vessels called capillaries, allowing blood to leak into surrounding tissues. The blood is what gives a bruise its initial black-and-blue color. That initial color is influenced by the loss of oxygen from hemoglobin, the molecule in blood that ferries oxygen from the lungs through the body. Oxygen-carrying hemoglobin causes blood to appear bright red, while oxygen-depleted hemoglobin turns blood bluish. In the blood that leaks into tissues after a heavy blow, hemoglobin rapidly loses its oxygen, turning bruises blue or purplish.
As bruises heal, the body breaks down spilled blood cells and their hemoglobin. The iron in hemoglobin ...
