How sweat keeps you cool in hot weather and 6 more fun facts: Shots


There’s nothing stinky about the salty sweat that drips off your face after a run. It’s just your body giving off otherwise dangerous heat.

Werayuth Tessrimuang/EyeEm/Getty Images


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Werayuth Tessrimuang/EyeEm/Getty Images


There’s nothing stinky about the salty sweat that drips off your face after a run. It’s just your body giving off otherwise dangerous heat.

Werayuth Tessrimuang/EyeEm/Getty Images

Phew, this summer was hot – and some places are still roasting! As people around the world experience dangerously high, record-breaking temperatures, we’ve all been sweating.

You might find sweating bothersome most of the time, but that salty fluid oozing from your skin is essential to keeping you cool. And there’s so much more to the brackish stuff than meets the eye.

Several NPR science staffers braved the heat this summer to shake off the sweat. These lessons are based on their reports:

1. Sweat keeps you cool by turning to gas

Let’s start with the basics. Sweat is mostly made up of water and salt secreted by millions of glands in your skin. These glands are basically coiled loops that help move some of the fluid moving through the spaces between your cells, bones, and organs up and out across the surface of the body.

When the sweat on your skin evaporates from a liquid to a gas, it absorbs with it some heat from the blood just under your skin. The now cooler blood then travels around your body and back to your heart, helping to keep all your internal parts at the right temperature to function.

2. Most sweats don’t stink

Perspiration is usually odorless – at least that’s the case with sweat running down your forehead and arms after a run. But something is different from the sweat in your armpits and groin making it stink. The sweat glands in these places are called apocrine glands and release a protein-rich form of sweat that is eaten by bacteria. It is the by-products of these bacteria, feeding on your sweat, that produce body odor.

3. The bacteria behind BO are actually your allies

Even if you’re worried about your smelly sweat, don’t go scrubbing yourself with antibacterial soap looking for fresh pits just yet. Body odor-causing microbes help protect your skin from dangerous pathogens and even help prevent eczema.

A light lather with regular mild soap should be enough to remove the stench, at least temporarily, without killing the bacteria.

4. Most Animals Don’t Sweat

Now let’s be clear. You are the sweatiest of them all. OK, well not just you, but all humans.

Scientists believe that our ancestors evolved sweat glands between 1.5 and 2.5 million years ago as we move from under the cool canopy of forests to grasslands and prairies, long before we developed our big brains.

But most other animals don’t sweat, and they have to find other ways to avoid overheating — by panting, for example — if they can’t find shade, a river, or a pool. As NPR’s Rebecca Hersher recounts in her rhyming exploration of the ways various creatures stay coollions at a Maryland zoo this scorching summer have been given an extra treat – frozen leeches – to help bring everyone’s temperature down.

5. A hot bath is better than a cold shower to avoid overheated nights

It may seem counterintuitive, but when you step out of a hot or lukewarm bath at night, researchers say, water evaporates from your skin, drawing heat away from your body and freshen up before going to bed. This life hack works best about an hour before bedtime, scientists told NPR reporter Joe Palca — and you’ll sleep better and deeper when you’re cooler.

6. Some insects look for salt in human sweat

Unfortunately for us, mosquitoes, along with many other insects, are attracted to human sweat. Insects need sodium from saltjust like all of us, and our salty sweat has what they need.

Scientists suspect that millions of years ago, some ancestors of sweat-drinking mosquitoes discovered that there was an even more nutritious substance under human skin: our blood. These blood-sucking biters gained an evolutionary advantage over non-biters and thrived.

7. Astronauts need extra help getting rid of body heat

Sweating can be a big problem for people in a low gravity environment like space because even after intense exertion, sweat does not exactly flow off the skin without gravity. Instead, it kind of just sits there and builds up, which can mess up electronic equipment and make spacewalks very uncomfortable.

Thus, astronauts wear special underwear during their spacewalks; it is filled with cooling tubes that evacuate the heat. A bonus in the controlled environment of a space station: any extra moisture from sweat that enters the air is sucked up by the ventilation system and recycled as fresh water for the astronauts to drink.

Reporting for this story was drawn from our summer sweat series by NPR’s Geoff Brumfiel, Ari Daniel, Michaeleen Doucleff, Nell Greenfieldboyce, Pien Huang, Rebecca Hersher, Joe Palca and Lauren Sommer. Still thirsty for sweeter sweat science? Brumfiel, Greenfieldboyce and Hersher recently spoke with the hosts of NPR’s Short Wave science podcast to answer other questions and share what they have learned.

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