Sweat

The human body is capable of keeping itself cool in extremely hot conditions. Our body's natural air conditioning? Sweat.

The principal of sweating is fairly straightforward. Your body secretes a liquid onto the surface of the skin. This liquid evaporates, taking heat from your body as it does so. The blood passes through this newly cooled skin and recirculates to the rest of the body, cooling it as it does so.

Sweat is necessary for survival in hot environments, but can turn deadly in the cold. Risk for hypothermia increases exponentially when you are wet. Much of survival is centered on keeping you dry, because if you are dry, you can keep yourself warm. You need to be extra careful of keeping yourself dry of your body's own coolant. If you are doing intense work in a very cold environment, building a snow cave for instance, or trudging through waist deep snow in snowshoes, every effort should be made to tailor your exertion to keep yourself from breaking sweat. Take frequent breaks and strip some layers if you begin to feel hot or warm.

Cold kills in the wilderness. And if you're wet, you're cold.