heat exhaustion : Preventing Heat-Related Illnesses

Your sweat is your body's main system for getting rid of extra heat. When you sweat, and the water evaporates from your skin, the heat that evaporates the sweat comes mainly from your skin. As long as blood is flowing properly to your skin, extra heat from the core of your body is "pumped" to the skin and removed by sweat evaporation. If you do not sweat enough, you cannot get rid of extra heat well, and you also can't get rid of heat as well if blood is not flowing to the skin. Dehydration will make it harder for you to cool of in two ways: if you are dehydrated you won't sweat as much, and your body will try to keep blood away from the skin to keep your blood pressure at the right level in the core of your body. But, since you lose water when you sweat, you must make up that water to keep from becoming dehydrated. If the air is humid, it's harder for your sweat to evaporate -- this means that your body cannot get rid of extra heat as well when it's muggy as it can when it's relatively dry. One way to determine the effect of humidity with high temeperature is the  heat index. 

The best fluid to drink when you are sweating is water. Although there is a little salt in your sweat, you don't really lose that much salt with your sweat, except in special circumstances; taking salt tablets may raise your body's sodium level to hazardous levels. (Your doctor can tell you whether or not you need extra salt.) "Sport drinks" such as Gatorade® will also work, but water is usually easier to obtain.

It's also important to be sensible about how much you exert yourself in hot weather. The hotter and more humid it is, the harder it will be for you to get rid of excess heat. The clothing you wear makes a difference, too: the less clothing you have on, and the lighter that clothing is, the easier you can cool off. Football players are notoriously prone to heat illness, since football uniforms cover nearly the whole body, and since football practice usually begins in late summer when the temperature outside is highest. Therefore, football players should pay extra attention to the fluids they drink and lose: teams and coaches should limit practice and wear light clothing for practice on very hot days, and athletes must be able to drink all the water they want during practice.