Dreyer says he sees a "fair number" of people with heat exhaustion who have been out on the baseball field or construction site for too long. But many victims of heat illness, particularly children, never get to the emergency room. "Quite a number of them are never diagnosed; they just go home feeling a little lousy, and they're real hot," he tells WebMD.
"If they're healthy, usually that's a self-limited disease. They get too tired to play, or they go home, or their mothers notice their faces are real red and they're sweating profusely and they take them home," Dreyer says.
Of course, there is a way around all this: water. It's important for everyone, but it takes on added importance for people working outside, whether they are paving roads or exercising.
David Martin has completed 29 marathons, and he's never, as he calls it, "bonked." But plenty of athletes, experienced or not, fade as they work out in temperatures high enough to make a kettle whistle.
Martin says he owes his successful track record to proper preparation -- especially the proper regulation of fluids. Of course, he also has an advantage over most people in that he has a PhD in physiology and is the chairman of sport science for U.S.A. Track and Field.
"I've always been sly enough and followed my principles of physiology," Martin tells WebMD. Those principles are quite simple, he says: If you're an athlete -- whether you're training for the Olympics or just jogging around the block -- "you really want to live a healthy lifestyle, which means not being thirsty and not being hungry."
Although avoiding the hottest parts of the day is best, that's not always possible. So week-long laborers and weekend warriors alike should make sure they never let themselves get thirsty.
"As soon as they have reached a point of thirst, they actually are dehydrated," Martin tells WebMD. "We say you never pass up a drinking fountain, or carry a small bottle and take sips to make sure your fluid levels are up."