Because human beings are best adapted to warm weather and ill-adapted to cold weather, hypothermia is a common occurrence. Physicians have been writing about hypothermia for centuries. Cold injury has had a major impact on political and military history.

Hypothermia occurs when heat loss exceeds heat production and is defined as a core body temperature below 95 degrees. At this temperature, the body no longer generates enough heat to maintain body functions. Mild hypothermia happens when the core temperature is above 90 degrees and severe hypothermia is when it is below 90 degrees. Exposure to cold can be acute (e.g., submersion in cold water), subacute (e.g., exposure to cold for 24 to 48 hours), or chronic (exposure longer than 48 hours).Wind and water chill and wet clothing are major factors in cold injury. Though hypothermia occurs more often in northern climes during winter months, it may also occur during the summer months, especially among those engaging in water activities. Lack of heating in the home is a fairly common factor, especially among the elderly.

Signs and symptoms include:

Mild hypothermia

- shivering

- lethargy

- slurred speech

- memory lapses

- fumbling hands

- cold abdomens and backs

Profound/severe hypothermia

- no shivering

- muscles may become stiff and rigid

- blue skin

- unconsciousness

First aid

The main goal in treating hypothermia is to rewarm the victim as safely and efficiently as possible. Available techniques include both passive and active methods.

Passive rewarming techniques rely on a victim's ability to generate heat. Allowing the victim to rewarm this way can be quite slow. Only passive methods are generally used by first aiders. Wet clothing should be removed and the victim insulated with layers of clothing and blankets.

If a victim has profound/severe hypothermia, aggressive external measures should not be used, especially on the limbs because surface rewarming leads to vasodilation (wider blood vessels). This can lead to an additional drop in blood pressure and also increase the amount of cold, acidotic limb blood returning to the core. This action is known as "afterdrop" and can decrease core temperature.

Any significant jostling can cause a heart arrhythmia (abnormal heart beat). Great care should be taken to avoid rough handling of the victim.


Layers of clothing help prevent hypothermia. The layer against the skin should be a material that both insulates and wicks away perspiration (silk, polypropylene or capilene, for example). The next insulation layer should be a garment made of wool or one incorporating polyester fleece or Thinsulate. Finally, an outer layer of nylon, Gore-Tex or Supplex may be needed to protect against the wind and shed water.

Overdressing can be dangerous, because perspiration may saturate clothes and greatly increase heat loss.

Hypothermia, a relatively common problem in winter months, can cause death. Treatment centers on rewarming the victim safely and efficiently. Care should be taken to avoid heart rhythm disturbances. Simple precautions greatly reduce the risk of hypothermia.

- Alton Thygerson is a professor of health sciences at Brigham Young University.