7 fun facts about sweat

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

You might find perspiration a nuisance most of the time, but that salty liquid oozing from your skin is key to keeping you cool. And there’s so much more to the briny stuff than meets the eye.

Several NPR science staffers braved the heat this summer to get the dirt on sweat. These lessons are based on their reporting:

1. Sweat keeps you cool by turning into a gas

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

When the sweat on your skin evaporates, transforming from a liquid into a gas, it takes some heat from the blood right under your skin with it. The now-cooler blood then travels around your body and back to your core, helping keep all your inner parts at the right temperature to function.

2. Most sweat doesn’t stink

Perspiration is mostly odorless — at least that’s true of the sweat dripping from your forehead and arms after a run. But something is different about the sweat from your armpits and groin that makes it stink. The sweat glands in those places are called apocrine glands, and they release a protein-rich form of perspiration that gets eaten by bacteria. It’s the byproducts 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 in pursuit of fresh pits just yet. The microbes that give rise to body odor help protect your skin from dangerous pathogens and even help prevent eczema.

A light sudsing with regular gentle soap should be enough to knock down the stink, at least temporarily, without wiping out bacterial pals.

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 think our ancestors evolved sweat glands between 1.5 million and 2.5 million years ago as we moved from under the cool canopy of the forests into the grasslands and prairies, long before we evolved our big brains.

But most other animals don’t sweat, and they need to find other ways to keep from overheating — through 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 cool, lions in a Maryland zoo this steamy summer got an extra treat — frozen bloodsicles — to help lower everyone’s temperature.

5. A warm bath is better than a cold shower to prevent overheated nights

It may seem counterintuitive, but when you get out of a warm or lukewarm evening bath, researchers say, the water evaporates from your skin, pulling heat from your body and cooling you down before you go to sleep. This life hack works best about an hour before bedtime, scientists told NPR reporter Joe Palca — and you’ll sleep better and more deeply when you’re cooler.

6. Some insects seek the salt in human sweat

Unfortunately for us, mosquitoes, along with many other insects, are attracted to human sweat. Insects need the sodium in salt, just like the rest of us, and our salty perspiration has what they need.

Scientists suspect that millions of years ago, some sweat-drinking ancestors of mosquitoes discovered there was an even more nutritious substance beneath human skin — our blood. Those bloodsucking biters gained an evolutionary edge over the nonbiters and thrived.

7. Astronauts need extra help to get rid of body heat

Perspiration can be a big problem for people in a low-gravity environment such as space because, even after great exertion, sweat doesn’t exactly drip off the skin without gravity. Instead, it just kind of sits there and pools up, which can disrupt electronic equipment and make spacewalks extra-uncomfortable.

So astronauts wear special underwear on their spacewalks; it’s filled with cooling tubes that whisk the heat away. One bonus in the controlled environment of a space station: Any extra moisture from sweat that does get into the air is sucked up by the ventilation system and recycled into fresh water for the astronauts to drink.

Reporting for this story was drawn from our summer series on sweat by NPR’s Geoff Brumfiel, Ari Daniel, Michaeleen Doucleff, Nell Greenfieldboyce, Pien Huang, Rebecca Hersher, Joe Palca and Lauren Sommer. Still thirsty for more sweet sweat science? Brumfiel, Greenfieldboyce and Hersher sat down recently with the hosts of NPR’s science podcast Short Wave to take more questions and spill what they’ve learned.