6 Weird Things You Didn't Know About Sweating

"There are two main reasons. One is that as you improve your fitness, you tend to exercise more intensely, which can make you sweat more," explains Mary Beth Brown, Ph.D., an assistant professor in the Department of Physical Therapy at Indiana University. "The other is that you get better at sweating the more you do it." You'll start perspiring earlier in your work­ out, and more of your sweat glands will be activated to help rid your body of excess heat.

But keep in mind sweat isn't the only measure of how hard you're working—some work­ outs leave you less drenched simply because of the nature of the moves. "How much you sweat is tied to many factors, including what type of activity you're doing, your age, and your genetics," says Kory Gill, M.D., a sports medicine specialist at the Texas A&M Health Science Center. A better indicator of your performance is how difficult it is to talk midway through an activity. During a moderate­ intensity workout, you should be able to speak in broken sen­tences; during vigorous exercise, you should be able to manage only a few words at a time. (BTW there is such a thing as excessive sweating. Here's what you need to know.)

"Sweat contains salt, which can irritate the eyes. Plus, it's slightly acidic compared with the eye's fluid," Brown explains.

Fortunately, there's no evidence that salt from sweat can harm your eyes, says Stephanie Marioneaux, M.D., a spokeswoman for the American Academy of Ophthalmology. If perspiration is interfering with your workout, wear a sweat­ band or a moisture­-wicking hat or visor to trap forehead mois­ture before it has a chance to creep down into your eyes. Keep artificial tears on hand to use if you do get an errant drop. (Some good news: sweat spreads happiness! No, really.)

Cranking up the thermostat in the studio has only modest perks. "Some people find that the heat improves their flexibility and range of motion, making it easier to get into poses," says Cedric X. Bryant, Ph.D., the chief science officer for the American Council on Exercise, who has studied hot yoga. If you're hop­ing to sweat off a few pounds, though, forget it. Bryant says that the difference in calorie burn between the two types of yoga is almost negligible.

While most healthy people should be able to make it just fine through a 90 minute hot­ yoga class, the room's humid­ity poses some risk. "When humidity is high, sweat stays on the skin and doesn't evaporate. That reduces your body's ability to cool itself," Bryant says. "To stay safe, drink cold water every 15 min­utes or so to help keep your core temperature out of the danger zone." If you're doing hot yoga for more than an hour straight, swap water for an electrolyte­-spiked sports drink to make up for the sodium and potassium you're sweat­ing out. And if you start feeling dizzy or nauseated or develop a headache, leave the room immediately to get some cool air.

Be especially careful during Bikram yoga, which is more extreme than regular hot classes: Rooms are kept at 105 degrees with 40 percent humidity. (Hot­ yoga classes are typically 90 to 95 degrees with no set humid­ity.) Bryant advises starting with shorter, cooler classes and work ing your way up to a full-­length Bikram session. (Here's more on the heated vs. cool fitness class debate.)

"When you stop exercising, your body continues to generate heat to fuel functions like restocking your energy stores and redistributing your blood flow," Brown explains. As a result, your core temperature can stay elevated, triggering perspiration even postshower.

To cool down and dry off quicker, you should actually refrain from taking a super cold shower or splashing icy water on your face. "The chilly temp constricts your blood vessels, causing hot blood from your skin to rush to your core, raising your body temperature," says hydration expert Stacy Sims, Ph.D., an exercise physiologist in San Francisco. Instead, when you're done exercising, take a coolish (not freezing) shower, then stand in front of a fan to evaporate any lingering sweat before it beads up.

In addition, sip ice-cold water before and during your workout, Sims suggests. Her research found that this minimizes the rise in your core temperature, so you'll stop sweating sooner.

"Yes and no," says Juan Del Coso, Ph.D., a professor of human physiology and exercise at Universidad Camila José Cela in Spain, who has studied the issue. "When you sweat more, you do lose some toxins, but not enough to have a measurable health benefit." If your body needs to get rid of something noxious, your kidneys flush it into your urine, not your sweat.

In fact, hitting the sauna after a hangover can backfire. "When you force your body to perspire, your kidneys respond by trying to conserve water, so you urinate less, which can make you hang on to toxins," Bryant explains. You're better off drinking plenty of water and eating veggies with a high H20 content to recover after a rough night.

Blame your prehistoric ancestors. Unlike the sweat you produce at the gym, which is mostly water, the type you pump out during anxiety- provoking situations is laced with pheromones that stimulate your amygdala, the area of the brain that controls your fight-or-flight response, according to research from Stony Brook University. This probably evolved to help protect us from danger: If a fellow cavewoman saw a tiger or other predator and couldn't call out to warn you, a whiff of her nervous sweat would give you a heads- up that something was wrong, says Lilianne R. Mujica-Parodi, Ph.D., the author of the study.

The last thing you want is for your pheromone- packed sweat to broad- cast "She's freaking out!" when you're trying to play it cool during a job inter- view or a blind date. So don't stop at your under- arms when it comes to applying antiperspirant— also hit around your groin, where apocrine glands produce nervous sweat, Mujica-Parodi says.

Also try working up a sweat at the gym before the stressful event, Mujica-Parodi suggests. When you're anxious, your levels of the stress hormone cortisol rise in order to give you energy to fight or run away. "But today most stressors don't involve fighting or fleeing, and the extra cortisol only makes you more nervous and reduces your ability to think analytically," she says. Exercising gets rid of the excess so you can stay focused—and dry— when it counts.