I can’t find an authority to back me up on this, but I’d be willing to wager that Texas will produce more human perspiration than any other state this summer, because we have not only a large population—literally, more sweaters—but more months to work up a good one (these days, June to October, minimum). In fact, while I never hear my New York friends discussing their summer stickiness, here it’s a conversation in and of itself: My wife, for example, likes to brag that she’ll barely break a sweat on a five-mile hike in August (true), while my friend David complains of ruining a dress shirt just by eating a chile relleno on an 80-degree afternoon (also true). Yep, sweating in Texas isn’t just biological, it’s cultural. I kid, of course—but really it’s no laughing matter, not if you consider sweat’s pivotal connection to a graver hot-weather affliction: dehydration. This, and an overall malfunction of the body’s cooling system, is a common reason Texans visit the ER every summer. So, actually, why not talk sweat? To stay healthy in the heat, it pays to understand your internal waterworks.
Amazing but true: We have roughly 2.6 million sweat glands in our bodies; they are everywhere except the lips, the nipples, and certain genital areas. They help control our body temperature and come in two varieties: eccrine glands, which inhabit most of the surface of the body, and apocrine glands, which are mainly confined to the armpits and anal area. The former, which find their end point at our pores, produce perspiration that is mostly water and includes some sodium. The latter, which tend to end at our hair follicles, produce a fluid that also includes proteins and fatty acids, whose eventual breakdown (by bacteria on our skin) causes its yellowish hue and, er, distinctive odor.
How’s it all work? In both cases, the sweat gland operates like a tiny pump; it has a coil at its base and a tube that runs to the skin’s surface. When the body heats up—because of external heat, internal stress, or exercise—our blood vessels dilate, and this inevitably forces a portion of our plasma (the fluid that is the basis of blood) out into the space between our cells. Here it combines with interstitial fluid (the stuff our cells are bathed in) and is gathered by the sweat glands, which push it up to the skin’s exterior.
You then begin to cool: Evaporation as a process requires its own heat, so as the sweat leaves your body, it takes some heat with it. (This is why when it’s really humid the cooling system doesn’t work as well. Your sweat just sits there.)
Water, water everywhere.
The system is based on a constant supply of water, so if you don’t watch the fluids, it gets screwed up—kind of like your car does when you don’t keep water in the radiator. (The adult body is 50 to 60 percent water; a portion of that is the plasma in our blood, which is 90 percent water.) And it doesn’t take long for this to become dangerous: Once dehydration takes over, you can spiral into heat exhaustion—with muscle cramps, nausea, and disorientation—and then into heatstroke, which is life-threatening because your body’s heat-controlling mechanism (that sweat pump and evaporation thing) is not merely impaired but shuts down. Your body temperature can rise to 105 degrees, and the internal software is helpless to stop it.
So the key is to pre-hydrate: Always have enough water in your system to sustain the tasks you’re performing. The average person loses about ten cups (eighty ounces) of fluid a day just through normal sweating and excretion. This is where the long-held belief came from that we all need to drink eight to ten glasses of water a day. But because we replace at least half of that just through the food we eat, this maxim has now been pretty well relegated to the orbit of bunkum. How much to drink? Four to six glasses. Since three of those will probably come with meals, we’re talking basically one extra glass a day.
Of course, if you’re exercising, the stakes go up. Paul Pepe, the chief of emergency medicine at Dallas’s University of Texas Southwestern Medical Center and Parkland Memorial Hospital—which see hundreds of cases of dehydration each summer—says a good rule of thumb is to hydrate to the point that you need to urinate; do so, and the remaining fluid in your system should sustain a strenuous, hour-long workout. His colleague Luis Palacios, a family and sports-medicine specialist at UT Southwestern, is a bit more precise. He suggests replenishing with 400 to 800 milliliters (about 12 to 24 ounces) of water for every hour of exercise.
Sports drinks: magical elixirs or snake oil?
When Gatorade first showed up, in the sixties, it was hailed as the antidote to dehydration—a sports drink that tasted good, replenished fluid and sodium, and even included some carbs for energy. But then came the questions: Was the stuff really any better at fluid maintenance than water? Was the sodium in it dangerous to folks with hypertension? Did the carb content add pounds? Lona Sandon, an assistant professor at UT Southwestern and a spokesperson for the American Dietetic Association, tells me that sports drinks have actually gotten a bum rap. They do replenish fluid as well as water—actually better, she says. Though drinking a glass of water may quench your thirst, it may not replenish enough fluid; the sodium in a sports drink makes you more thirsty and encourages more fluid intake. She recommends sports drinks mainly for strenuous, high-sweat outdoor exercise and that you select one with fourteen to sixteen grams of carbohydrates and a hundred milligrams of sodium per eight-ounce serving. A couple of other things: First, if you do have high blood pressure, watch your consumption, as the sodium will aggravate that condition. Second, Sandon says, if you notice salt caking on your skin or clothing after exercise, you’d be wise to ramp up to a