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Why sweat shouldn’t get you hot and bothered

A presidential guard wipes the sweat from his colleague in front of the Tomb of the Unknown Soldier in Athens, Greece, on Aug. 3. Temperatures reached as high as 107 in the city.  (Michael Varaklas/Associated Press)
A presidential guard wipes the sweat from his colleague in front of the Tomb of the Unknown Soldier in Athens, Greece, on Aug. 3. Temperatures reached as high as 107 in the city. (Michael Varaklas/Associated Press)
By Jill U. Adams Special to the Washington Post

Perhaps you have mixed feelings about sweat. Or maybe you’re solidly on Team Yuck. “Sweat kind of gets a bad rap,” says Lindsay Baker, an exercise physiologist at the Gatorade Sports Science Institute in Barrington, Ill. “But it’s a good thing.” That’s because sweat is the human body’s terrifically efficient way of cooling down when you’re outside in 90-degree weather or when you exercise.

Our ability to sweat has allowed humans to thrive in hot climates and to be able to be physically active during daytime hours. “It’s humanity’s superpower,” says Sarah Everts, author of “The Joy of Sweat: The Strange Science of Perspiration.” That’s because fur-covered animals either don’t sweat or are limited to sweating on their paws only.

We sweat when we’re hot, when we’re physically active and when we’re stressed, anxious or scared. Emotion-triggered sweating occurs mostly on our palms, soles and foreheads. It’s part of the fight-or-flight response. The same sweaty palms you may want to hide were thought to help mammals get a bit more of a grip on surfaces as they ran or climbed away from danger.

As for cooling, however, Everts says, “We’re the naked ape.” Referring to the large surface area of skin that people have to cool with sweat evaporating, she says, “We have all this real estate.” So, sweat makes us human – as much as our ability to make tools or to laugh. But you might still say so what? Sweat is still gross.

We have sweat glands all over our body, and most of them produce salty, watery sweat. Those are the main ingredients – water and sodium chloride – and they come from the watery component of our blood. Anything that’s circulating in our blood might also be present in sweat: metabolites such as lactic acid; drugs such as alcohol; and food constituents such as the odoriferous compounds in garlic.

But the idea that you can “sweat out toxins” is misleading. It’s true that any toxins circulating in your blood will probably show up in sweat. However, because only a tiny amount of your blood volume is excreted, only a tiny portion of toxins are released. Because the blood plasma carries this stuff – be it good stuff like glucose or amino acids or bad stuff like heavy metals and urea – you can’t get all those bits out of the body without completely dehydrating, Everts says.

“It’s not a very effective way to excrete toxins from the body,” Baker says of sweat. And, she says, our bodies do have detox systems, with the liver, kidney and gastrointestinal tract taking primary roles. The sweat on your arms may carry tiny whiffs of scent, but your armpits are the main source of odor. That’s because there are two types of sweat glands present there.

There are eccrine glands, which sweat out the salty, watery stuff discussed above, and apocrine glands, which release a viscous, waxy substance. The waxy stuff is odorless by itself, but when you sweat, the bacteria on your skin feasts upon it to create body odor. People who don’t want to share their body odor with others may use deodorant to prevent the smell or antiperspirant to prevent sweat itself.

Deodorants contain components that are toxic to bacteria, making the armpit a hostile environment for the stink producers. Antiperspirants plug sweat glands, thereby preventing sweat from reaching the surface of the skin. If you apply these products only on your armpits, you’re not going to stop sweat’s cooling function because you have sweat glands all over your body. The actual cooling offered by armpit sweat glands pales in comparison to the rest of the body.

Deodorants and antiperspirants might also be scented to cover any residual odor. On her book tour, Everts has had many people share their “sweaty confidentials,” including those who use antiperspirant on other sweaty places such as their foreheads or high on their thighs. Baker recently reviewed the state of research on sweat for the scientific journal Temperature.

Her interest since graduate school has been to better understand what is lost through sweat during exercise and what may need replenishing, an interest that Gatorade shares. She conducts research in controlled lab settings to test athletes’ needs under different climate conditions. Even though sweat is mostly water and salt, the sodium chloride concentration varies a lot among individuals. So can other electrolytes such as potassium, magnesium and calcium.

With training, athletes tend to sweat sooner – the body apparently becoming more proactive about cooling. Endurance athletes adapt in such a way to conserve their body’s sodium, with smaller amounts present in their sweat than in the rest of us, Baker says. Many people are interested in monitoring lactic acid in sweat, which might indicate a switch from aerobic to anaerobic metabolism during sustained exercise.

But measuring this substance in sweat is hardly straightforward, Baker says. There’s individual variation, and there are confounding factors – for instance, the measured amount includes lactate produced by the sweat glands in addition to the amount coming from working muscles.

As the heat waves of summer come and go, perhaps we can come to appreciate our sweaty selves a bit more. And when it’s really hot, you can help your body out by keeping it hydrated (supplying the water for sweat), exposing your skin (making sweat available to evaporate into the air) and using a fan or finding a breeze to speed evaporation of sweat.

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