Sweating is a bodily function that used to be taboo, with women in particular being told they don’t sweat, they glow. But look at any fashion magazine or beauty blog today, and you’ll find that sweat is in style. From infrared saunas to hot yoga, towel-soaking activities are being touted not only as relaxation tools, but also as ways to stay healthy by flushing out toxins.
Too bad you can’t sweat away toxins any more than you can sweat actual bullets. Recently published calculations back up what scientists have been screaming into their pillows for years: Sweating out toxins is a myth.
Humans sweat to cool ourselves, not to excrete waste products or clear toxic substances. That’s what our kidneys and liver are for. Of course, there’s usually some grain of truth at the heart of a myth, and toxic sweat is no exception. While sweat is made up mostly of water and minerals, it can contain trace amounts of various toxic substances.
But the new findings, published in the journal Environment International, show that even when we do excrete environmental pollutants through our pores, the amounts we can sweat out are minuscule.
“You always have to ask how much,” says chemist Joe Schwarcz. “When you look at sweat, you can find many substances, [but] the presence of a chemical cannot be equated to the presence of risk.”
Athletes warm up in a sauna during the Lofoten Masters, the world's most northerly surf competition.
PHOTOGRAPH BY OLIVIER MORIN, AFP , GETTY IMAGES
A high school wrestler uses a sauna during a tournament.
PHOTOGRAPH BY JOE AMON, THE DENVER POST, GETTY IMAGES
Is Sweat Toxic?
Schwarcz directs McGill University’s Office for Science and Society, which debunks science myths, and he says the group is inundated with questions about medical scams and quackery, including many that promise to “detoxify” the body.
So, what are the levels of harmful substances in sweat?
For most pollutants, they’re so low that they’re essentially meaningless, says Pascal Imbeault, who led the new study. Imbeault is an exercise physiologist at the University of Ottawa in Canada who’s studying pollutants that are stored in body fat. Known as persistent organic pollutants, these include pesticides, flame retardants, and now-banned polychlorinated biphenyls, or PCBs, which are still found in the environment.
These are the kinds of chemicals that many people think of as “toxins” in our food and environment. (Imbeault adds that we’re actually using the wrong word—they’re toxicants. Toxins are natural substances made by plants and animals.)
Because these chemicals are attracted to fat, they don’t dissolve well in sweat, which is mostly made of water.
At most, Imbeault and his colleagues found, a typical person doing 45 minutes of high-intensity exercise a day could sweat a total of two litres a day—normal background perspiration included—and all that sweat would contain less than one-tenth of a nanogram of these pollutants.
To put that in perspective, “the amount in sweat is 0.02 percent of what you ingest every day on a typical diet,” Imbeault says. If you really pushed it on your exercise regime, you might release up to 0.04 percent of your average daily intake of pollutants.
What that means is that there’s no way you could sweat enough to get rid of even one percent of what you’ll eat in your food that day.
Keep in mind, the levels of pesticides and other pollutants in most people’s bodies are also extremely low to begin with. It’s a testament to analytical chemists that we can detect a compound down to parts per trillion, Schwarcz says, but that doesn’t mean it’s harming you or that incrementally decreasing it will have any health effect.
A woman looks out from a sauna window as she relaxes after a swim at Brockwell Lido in London, England.
PHOTOGRAPH BY CARL COURT, GETTY IMAGES
Sweating It Out
Back to that grain of truth: Small amounts of heavy metals and BPA from plastics do make their way into sweat, because these pollutants dissolve more readily in water. But there are more effective ways to remove high levels of metals from the blood, such as chelation therapy. And you pass more BPA out of your body in urine than in sweat. The best way to reduce your BPA exposure is to avoid eating and drinking out of containers made with it, according to the National Institute of Environmental Health Sciences.
Of course, none of this has stopped a growing sweat-detox industry. The latest fad is infrared saunas, which use infrared lights as a heat source instead of electric heaters or steam. When a writer at The Atlantic looked into the detoxification claims made for these saunas, it quickly became apparent they weren’t based on any actual science.
Yet spas and sauna makers continue to assert their detox benefits. Fire departments in Texas and Indiana have even bought infrared saunas on the premise that firefighters will sweat out chemicals they’re exposed to in smoke, and that this will prevent cancer. While saunas may be soothing and have other benefits, the cancer-prevention claim has not been proven.
Taken too far, sweat therapy can even be deadly.
A 35-year-old woman in Quebec died after a detoxification spa treatment plastered her with mud, then wrapped her in plastic and put a cardboard box over her head. She lay under blankets for nine hours, sweating. Hours after the treatment, she was dead from extreme overheating.
“It’s the old story of wanting to provide a simple solution to a complex problem,” Schwarcz says. “Hope is so precious, but some people use hope for selling crazy stuff to people who are vulnerable.”
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Lead Image: A woman enjoys an infrared sauna in New York City. While such experiences can have a variety of benefits, claims that they help people sweat out toxins are not backed up by science. PHOTOGRAPH BY LAUREL GOLIO, REDUX