frostbite (chilblains), injury to the tissue caused by exposure to cold, usually affecting the extremities of the body, such as the hands, feet, ears, or nose. Extreme cold causes the small blood vessels in the extremities to constrict. The blood circulates more slowly and stagnation results. Eventually the body fluids may freeze. The condition is aggravated by tight clothing, physical inactivity, and dampness. Severe frostbite that is not treated may result in gangrene; amputation of the affected part may be necessary. See first aid.