Medical literature contains few if any cases in which people have recovered after their inner, or core, temperatures dropped below 55 degrees Fahrenheit. Core body temperature is usually measured by electronic sensors inserted into the digestive tract, often by way of the mouth or rectum. It cannot be be measured with an ordinary oral thermometer. Hypothermia is considered to exist whenever the core temperature is below 95 degrees. Hypothermia occurs when the body loses heat faster than it can burn fuel to replace it.
Age increases the risk for several reasons.
Exposed skin, cold air, cold water, cold wet clothing and sitting on a cold surface that conducts heat away from the body all greatly increase the rate of heat loss. Dehydration also adds to the risks. The rates of chemical activity in the body are slowed by very low temperatures. Eventually, the heartbeat and breathing may stop, but even a very slow heartbeat and rate of respiration may maintain vital body functions. Immediate treatment for hypothermia victims involves stopping further loss of heat by wrapping the person in warm dry blankets.