Working in the heat

A couple of interesting facts about working in the heat: sweat does not evaporate from the skin when the humidity is above 75%. Also, a person will get "used to" working in hot weather. This is not a psychological change, but an physiological one. After being exposed to hot temperatures for seven to ten days the human body becomes more efficent at cooling itself. Sweat production can increase from about one liter an hour up to three. In addition, sweat glands begin functioning at a lower temperature and their ability to reabsorb salts will increase, leading to better heat dissipation.

It's vitally important to replace that potential three liters of fluid, of course. Water and sports drinks are best (in fact, diluted sports drinks are better than regular). If I'm drinking nothing but water, I always crave sunflower seeds, as their salty coating replaces the electrolytes I'm losing.

Much more very clinical information is available at eMedicine.