Hypothermia is caused by a body being exposed to a cold environment without appropriate clothing or other protection. It is generally defined by a body temperature below 90 degrees Fahrenheit. It can be brought on more quickly by immersion in cold water, where the body temperature can drop several degrees in a matter of minutes. Although several mammals (during hibernation) and most reptiles can survive for long periods of time at that body temperature, prolonged hypothermia will lead to death by organ failure.
The body fights hypothermia by cutting of blood flow to the limbs to retain heat in the torso and head to protect the vital organs. This results in lose of co-ordination in the limbs and lose of dexterity in the hands. The hands and feet will also start to lose sensation. The body will also start to shiver to generate more heat.
Treatment is by application of heat to patient. Warming should be done as soon as possible, preferably by placing the body in warm water.
Hypothermia is occasionally induced by physicians in controlled circumstances as it will slow the brain's need for oxygen and allow a lower flow of blood to the brain without resulting in brain death. Cryosurgery is used to treat such conditions as an aneurysm in the blood vessels leading to the brain.