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What Good Is Sweat?

Perspiration isn't generally considered desirable. It makes clothes wet and uncomfortable, it makes our skin unpleasant to touch and it often smells bad. But the biological fact is that sweating is essential to good health, especially during exercise.

Why?

Humans take in and use water for a number of important physiological functions. It provides a medium for cells and tissues. It makes possible the transport throughout the body of important elements or compounds like sodium and sugar not to mention forming part of the blood that moves them. It provides structural cohesion and lubrication between all parts. But there's one more highly important function it helps perform: temperature control.

Homeostasis is the body's ability to keep certain processes and factors in equilibrium, this is not too far from a central point. Body temperature is one key item among those. When body temperature gets too high, we experience fever and ultimately heat stroke. If it's too low, we get chills. Both are signs that the body is in a less than ideal state.

One major reason is that all chemical reactions within the body have to take place within a very narrow range in terms of rate. Compounds have to be used and produced at just the right quantities within a certain time in order to proceed properly, or at all. Temperature, for very basic physical chemistry reasons, is a key factor in controlling that rate.

So how does sweat play a role in that?

Perspiring does not occur primarily in order to keep the amount of fluid in homeostasis - urination does that, along with breathing (though sweating plays a small part). But it has a huge effect on body temperature. As we exercise, chemical reactions speed up and mechanical motion is taking place. Both those produce more heat energy, which raises the internal temperature.

But the body is constantly seeking homeostasis - an equilibrium within a narrow range around a central point. For humans, that's 98.6F/37C on average - a small deviation is within normal range. As we sweat, the excess heat energy is moved from inside the body to the outside, along the surface of the skin, carried along with the perspiration.

Outside the body a physical principle is at work - Newton's Law of Cooling. Inside too, but never mind for now. Ignoring advanced mathematics, it says essentially that warmer bodies lose heat to cooler ones. We get cooler, the air gets a little warmer. Air molecules collide with the sweat molecules and pick up some of the heat energy they contain. That lowers the temperature of the sweat, lowering our temperature in the process (on the outside).

The net effect is to take excess heat on the inside and move it to the outside, somewhat like a home air conditioner or a car radiator. That helps keep the internal temperature at a constant 98.6F/37C.

That process takes place with breathing and just simple exposure. But sweating makes the process much more efficient, since water can carry a lot more heat than air does alone.

So, though it may have its unpleasant aspects, be thankful you perspire. After all, if you lacked sweat glands like your dog does, you'd look very silly panting.