Ever few years, the Center for Disease Control and Prevention (CDC), tests people to see what toxins are in the body based on chemical exposure. After surveying a few thousand people, the CDC combined the chemicals they found for a total of 153 to which we are exposed, some of which are worse than others (CDC). Some of the worse ones were things like dioxin and uranium — things you don’t want floating around in your body.
Sweat is the body’s natural cooling system. That’s why you sweat when you’re exercising, have a fever, are anxious, or are just hot. You feet, hands, and underarms are the place where you sweat the most (MedlinePlus). Sweat is primarily water that your body is losing, but it also contains other things, like lactic acid, ammonium, urea, amino acid, and sugars (The Journal of Biological Chemistry).
If only this rumor were true, but unfortunately, it’s not entirely so. There have been some studies that shown that arsenic, cadmium, lead, and mercury, may be excreted in “appreciable amounts” through sweat, even matching the waste removal rate of urine (Journal of Environmental and Public Health). But there are also claims that sweat accounts for less than 1% of the removal of these in metal poisoning cases (LA Times). But overall, you can thank your liver and kidneys for waste removal more than sweat. You may feel good after you sweat, but it’s not because you’re detoxifying.
Exercise and exertion can do great things for your skin because they increase blood flow, but sweat doesn’t take toxins out of the body. Though there are trace amounts of metals and other toxins, these aren’t comparable to the work your waste-removing kidneys and liver do. And to keep those (particularly the kidneys) optimal, you’ll want to make sure you replenish everything you sweat out.