Hypothermia — How Do You Lose Body Warmth?

Hypothermia moves quickly against the unprotected and unprepared, and it is not just a cold-weather problem. It can happen in mild temperatures, if conditions are right. Succumbing to hypothermia is sometimes referred to as dying of exposure. It's the chilling of the body's core, the gradual extinguishing of the inner fire that keeps you alive.

During the process, the victim passes through a series of physiological and mental stages that diminish his ability to survive unless the process is stopped and then reversed. If the situation goes too far, it may become impossible to reverse the decline toward coma and death. Obviously, it's better to prevent hypothermia than to have to treat the problem in the field.

To prevent hypothermia, we need to understand the many ways we lose body warmth. It isn't only about falling through the ice or getting caught out in a snowstorm. It's a lot of little things that can drain the warmth of your life away from you.

1. Conduction — Body warmth is conducted away by direct contact with an object that is colder than your body temperature. Through conduction, your warmth is attracted to the colder object. The rule is to never touch anything cold with bare skin. And don't remain in contact with cold objects very long even if you are protected by clothing. Sitting on a cold rock, for example, will eventually drain away warmth even through the clothing that gets compressed between your warm body and the cold stone.
2. Convection — This is air movement that blows away from you the thin layer of warm air that surrounds your body as a result of your body's natural radiation of warmth. Even a slight breeze will displace that warm layer of air and replace it with cooler air that will then pull warmth from your body. The rule is to protect yourself from the wind. Wear clothing that traps a layer of "dead" air close to your body. That's the purpose of the air-trapping "loft" of an insulating layer. 
3. Evaporation — One of the most certain factors in hypothermia is becoming wet.  It doesn't really matter whether the dampness comes as a result of a soaking rain, melting snow, falling through the ice, or excessive perspiration.  The point is, you're wet, and that's all that counts.  Staying dry should be among the highest priorities, and that means paying attention to your own level of perspiration.  The rule is, don't work yourself into a sweat, and the way you dress can help reduce excess perspiration. NOTE: in hot weather, evaporation works in your favor to cool your body, helping to prevent heat-related injury. 
4. Radiation — Radiant heat is what you feel from a fire. As a product of metabolism, your body has its own inner fire that naturally radiates warmth. There's nothing you can do to stop that type of energy drain as long as you're alive. The key to survival is to control the loss of radiant heat by using methods that trap it and direct it back toward you. An example is the use of an emergency blanket that has shiny foil on one side to reflect the warmth back toward you. Some articles of clothing are manufactured with reflective materials inside for this purpose. 
5. Respiration — As long as you're breathing (specifically exhaling), you're losing body warmth into the atmosphere. And when you inhale, you draw in cool air that absorbs warmth from the depths of your lungs, only to be exhaled and carry that warmth with it. In severe cold weather, you can help reduce this threat by inhaling warm air that is trapped inside your jacket. You could exhale it back inside, to preserve that warmth. The only complication is that there is moisture in your exhaled air, and you don't want to trap that moisture in your clothing or you'll soon have problems with #3, evaporation. 
6. Elimination — Often overlooked is the fact that when you eliminate waste as a result of digestion, it carries with it some warmth from inside your body. Not much you can do about that. 

Oh, yes, and while on the subject of hypothermia, recognize that dehydration and exhaustion both contribute to hypothermia. So, keep yourself hydrated  (especially challenging during cool weather when you don't naturally feel thirsty), and monitor your energy expenditure to make sure you don't get exhausted.  Eat high-calorie foods to keep the inner fires of metabolism burning. Intake warm drinks and hot food as often as possible, to add warmth to the core.