That would be nice. But for the most part, it's not true.
The liver and kidneys cleanse the body of the nasty stuff. Sweat? It has little to do with scrubbing the body of unwanted who-knows-what: the pollution we breathe every day; the pesticides we eat with our celery and strawberries; the remnants of a booze-bloated weekend.
"The amount that comes out in sweat wouldn't put a dent in what the body handles in a normal day," said Lawrence Spriet, a professor at the University of Guelph in Canada who studies, among other things, how hockey players sweat.
Sweating, he said, "would be an unreliable way to get rid of things."
Nevertheless, sweating is important stuff. With the season of sweat officially upon us, we might curse our damp work shirts, our wet hair, the way our jeans stick to our legs. But we should be thankful for our sweat.
The operators of CorePower Yoga, a Denver-based company with yoga studios around the country, celebrate the wet stuff. They keep some of their studios at around 100 degrees, with high humidity.
"We like to sweat," said Holly Brewer, a company spokeswoman. "People sweat and they are burning calories, and there is an intensity of the experience that keeps them coming back for more. There is a perception it is doing the body good."
It's more than mere perception.
If it weren't for sweating, we couldn't exercise. In addition, we would have a tough time, in this country, living anywhere outside of the the nation's far northern fringes. Goodbye, San Diego. Hello, Fargo—unless it's Fargo during a heat wave.
Sweating regulates the temperature of our bodies.
"If you don't have sweat on your skin, you will die of heat stroke," eventually, if your body temperature is rising, said Robert Dellavalle, a professor of dermatology at the University of Colorado.
Here's how it works: When the body senses increasing heat, through exercise or just ambient temperature, its thermoregulatory system—the complicated network that controls body temperature—opens up blood vessels to the skin. This permits heat to escape through the millions of sweat glands on the skin—a fabric of tiny ducts. The palms of the hands and soles of the feet contain the highest density of sweat glands.
Meanwhile, the sweat glands extract water and salt from the blood plasma that is constantly circulating through our bodies. The glands then press the liquid to the surface of the skin. When the water evaporates, cooling happens.
"It's a wild system," said Spriet. "On the one hand, we need the heat our body produces. But if you put me in a situation where I gain heat, I get in trouble and have to bring it down."
The system does, indeed, seem wild. And it has probably been instrumental in the spread of humanity around the globe.
"There are very few animals that sweat like we do, which is one reason we probably have been able to adapt to so many different temperatures," said Thad Wilson, a professor at Ohio University College of Osteopathic Medicine. "We are very, very good at sweating."
And we each sweat differently. Do your shirts or hats get caked in white after a big sweat? Then your sweat is more dense with salt than most people's—the white residue is salt. Salty sweaters are common, and they need to be attentive to hydration when they are exercising, said Spriet.
"If you are a doctor for a team, you are looking around for the guys who lose a lot of salt," he said. "They will be your crampers. You must work harder with them to make sure they replace their fluids and salt."
Spriet also said some people sweat heavily, and others are parsimonious with their perspiration. He has suited up hockey players with the same body size for tests, and sometimes one of the players will sweat twice as much as the other.
All of the sweat-drenched athletes have at least one thing going for them—by virtue of routinely raising their body temperatures through exercise, they have fine-tuned their powers of sweating.
A person will sweat, copiously, the first time she steps into a 100-degree hot-yoga studio. After doing hot yoga for two weeks, though, the sweating will commence more quickly, and the body will produce it in greater volume.
Why? During the weeks of practice, the body has adjusted to the sweltering room. It understands what is needed to maintain a healthy core temperature—sweat!—and begins pumping the stuff immediately.
Wherever, and however, you sweat, understand that while sweating for its own sake may not serve as a health tonic -- sorry about the toxins news—it could help with self-esteem, or just a sense of tidiness.
Go ahead and sweat for the good of your skin.
"A lot of people say they feel good when they have had a good sweat, and I agree," said Spriet. "It cleanses the skin. You have had activity through the sweat glands and it washes the pores of the skin."