Hypothermia is the intentional or accidental reduction of core body temperature to below 95°F (35°C) which, in severe instances, is fatal. Because humans are endothermic--warm-blooded creatures producing our own body heat--the core body temperature remains relatively constant at 98.6°F (37°C), even in fluctuating environmental temperatures. However, in extreme conditions, a healthy, physically fit person's core body temperature can rise considerably above this norm and cause heat stroke or fall below it far enough to cause hypothermia.

Intentional hypothermia is used in medicine in both regional and total-body cooling for organ and tissue protection, preservation, or destruction. Interrupted blood flow starves organs of oxygen and may cause permanent organ damage or death. The body's metabolic rate (the rate at which cells provide energy for the body's vital functioning) decreases 8% with each 1.8°F (1°C) reduction in core body temperature, thus requiring reduced amounts of...