Sweating Buckets... of SCIENCE! : Short Wave Sweating can be unpleasant, but consider the alternatives: You could roll around in mud. You could spend all day panting. You could have someone whip you up a blood popsicle. Sweating turns out to be pretty essential for human existence, AND arguably less gross than the ways other animals keep from overheating.

On today's episode, a small army of NPR science reporters joins host Emily Kwong to talk about how humans developed the unique ability to perspire, how sweat works in space and the neat things other animals do to beat the heat.

How have you (and the animals in your life) stayed cool this summer? Let us know at shortwave@npr.org.

Sweating Buckets... of SCIENCE!

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EMILY KWONG, HOST:

You're listening to SHORT WAVE from NPR.

Hey, SHORT WAVErs. I'm going to cut right to the chase. It has been hot. I'm in Alaska right now - yeah, to see friends, but honestly, to escape the muggy conditions of Washington, D.C. Well, lucky for me and for you, there's nothing like a nice layer of sweat to cool you down. If this is gross, do not push pause. Instead, thank evolution for doing you a solid - really a liquid - and meet this small army of sweat Avengers we've assembled to show you why sweat is sweet - or at least super interesting. I have three reporters with me - Geoff Brumfiel, Nell Greenfieldboyce and Rebecca Hersher. Geoff, I'm going to start with you because I heard that this harebrained idea of a series of sweat was yours?

GEOFF BRUMFIEL, BYLINE: It wasn't. It was Nell's.

NELL GREENFIELDBOYCE, BYLINE: Don't blame me.

KWONG: Oh.

GREENFIELDBOYCE: There was a list.

KWONG: Pointing fingers.

GREENFIELDBOYCE: There was a list of options, and we voted on it. And somehow, sweat won out.

BRUMFIEL: It's true. It's true.

KWONG: Why?

BRUMFIEL: Well, because sweat is really essential to being human. And also, it turns out it's really cool in a lot of other ways that we're just going to tell you today - a little bit about what we found out about sweat.

GREENFIELDBOYCE: And it's summer.

REBECCA HERSHER, BYLINE: Nothing says summer quite like sweat.

KWONG: Today on the show, our panel of sweats-perts give you a whole new perspective on your perspiration. You're listening to SHORT WAVE, the daily science podcast from NPR.

(SOUNDBITE OF MUSIC)

KWONG: All right. We are gathered here today to show some kindness to our pit stains and those beads of dew that form on your upper lip. As the most naked of the apes, we really have what I want you to now consider a superpower when it comes to full body sweat, courtesy of millions of eccrine sweat glands. And that was as much as I knew about sweat and, honestly, as far as I wanted to take this exploration, until now. Geoff Brumfiel, are we unique in this, we humans with our sweat?

BRUMFIEL: Yes, yes. I think it's fair to say that humans are uniquely sweaty, sweaty creatures. It's not just you. It's all 8 billion of us. And a lot of what I'm going to tell you is actually based on reporting by Joe Palca and Pien Huang, who are two correspondents who've also been looking into sweat.

KWONG: Shut up.

BRUMFIEL: So we have an enormous number of sweat glands on our body. And evolutionary biologists think that that probably is an essential adaptation for making us human. So chimpanzees, for example, a close relative, have sweat glands but mainly just in their hands, probably to help improve their grip. And, of course, the big difference between chimps and humans is that chimpanzees are forest dwellers, so they live in the shade, whereas we ventured out into sunnier climates and had to evolve better ways to keep cool. We could not depend as much...

KWONG: Oh, yeah.

BRUMFIEL: ...On the environment around us to cool us.

KWONG: So in what way did we develop sweat glands?

BRUMFIEL: The thought is that, literally, sweat is essential to human thermoregulation. Without sweat, we overheat and die as a species because we're large, warm-blooded animals. We can't discharge our heat without some help.

GREENFIELDBOYCE: But wait. Don't other large animals have to dissipate heat?

BRUMFIEL: Yes, Nell. So a lot of animals that have to discharge heat - let's take pigs, for example - they spend a lot of time rolling around in mud. And that is actually an alternative to sweating - is covering yourself in something else. You know, so sweat, to get back to kind of how it works, is - it's evaporative cooling, right? Like, so basically the water on your surface of your skin just carries away heat from your body as it evaporates, and that is a...

KWONG: It, like, wafts it away.

BRUMFIEL: Yeah. Yeah. It literally - the water molecules sort of take the heat off of your body, out of your body. So the blood near the surface of your skin is cooled. As it returns to the center of your body, it cools your core.

KWONG: Rebecca Hersher, what are some of the other ways that our fellow critters cool themselves off?

HERSHER: Well, I mean, just to build on what Geoff was saying, first of all, like, why doesn't it work to sweat if you're an animal?

KWONG: Yeah.

HERSHER: Mostly because you have hair or fur.

KWONG: Right.

HERSHER: So most animals are doing other stuff. The one that most people will be familiar with from the animals that live with them in their homes is panting, right? So that's - you'll see dogs doing it - tongue out. (Mimicking panting noise). Tons of animals pant. Your cat pants. Cows pant. You'll see like, like, frogs with their mouths open, trying to like, thermoregulate in that way.

KWONG: Oh, no way.

HERSHER: So yeah, it's just - it's an incredibly efficient way to affect your body temperature. And that's because there's a lot of moisture, obviously, right? Like all those membranes around your mouth. There's a lot of surface area, a lot of moisture and a lot of heat because it's, like, a tube to your innards. The last thing, Emily, that I think you will really appreciate is that one thing that zoos do with some of the really big animals, like, that Nell was talking about, like lions, right? - that is, like, a big, furry cat. And one thing that they do - the zookeepers do to keep them cool is they take leftover blood from their diet...

KWONG: Oh.

HERSHER: ...And they - do you want to guess?

KWONG: Do they let them roll around in it?

HERSHER: Gross. No.

KWONG: That makes no sense.

HERSHER: They freeze it. They freeze it into blood-sicles.

KWONG: What?

HERSHER: And then they give it to them.

KWONG: Oh, my God.

HERSHER: And the animals love it. And it's, like, really good for them.

KWONG: This is great. This is really cool. OK. We've covered people. We've covered animals. Let's go to space. Nell Greenfieldboyce, you have been looking at sweat in space. What happens up there?

GREENFIELDBOYCE: Yeah. I mean, people are fascinated by, like, you know, how you perform some of your basic biological functions in space. But I never saw people focus on sweat all that much. So I was interested in knowing, like, does sweat behave differently in microgravity? And so I talked with an astronaut who basically told me, yeah, it does. I mean, it's not like - you know, you won't be dripping with sweat in, like, the International Space Station because it won't drip down off your body. You know, it sort of, like, clings to your skin. Like, liquid and moisture in space, through surface tension, tends to cling to whatever it touches.

KWONG: Yeah, that sounds distinctly unpleasant.

GREENFIELDBOYCE: But, you know, that's all well and good when you're inside the space station. But when you go for a walk outside the space station and you're in one of those spacewalking spacesuits, which is, like, a little, mini spaceship that kind of fits around your body, you can't even touch your face. Like, you can't wipe yourself off with a towel. And those spacewalks are highly athletic events. So they're out there working for, like, seven hours. And heat control to keep you from sweating is a major issue because, like, the sweat - like where's it going to go, right?

And so they wear special cooling underwear that has like, little tubes of water to take the heat out. And they wear sweat bands and sweat-absorbing gloves. So it's different. It's very different. And another way it's different is they recycle sweat up there. So on the space station, water is a scarce resource, and so all the water gets recycled. And that includes sweat. And so I spoke with the water subsystems manager for NASA, who was telling me that each crew member...

KWONG: Yeah.

GREENFIELDBOYCE: ...Just through like, sweating and, like, breathing out moisture, puts out like, a liter and a half of water a day. And that all gets collected as water vapor by the air-handling system. And they basically clean it and recycle it. And so people drink it, and then they just, like, sweat it out again.

HERSHER: Oh, my God. I wonder if that means that they know who the sweatiest astronauts are, just by looking at the numbers.

BRUMFIEL: (Laughter).

GREENFIELDBOYCE: You know, we all get water from the tap, you know, that's often been through, like, a municipal water system. So it's not so crazy that you're drinking, you know, cleaned and recycled water. But the difference is, on the space station, like, you know, whose sweat you're drinking, right?

BRUMFIEL: Oh, my, God.

GREENFIELDBOYCE: Like, you're all there together. And so, like, you know, like, if we were all in the space station, we would be drinking each other's cleaned sweat, to say nothing of our cleaned urine. But that's - you know, that's a different issue.

KWONG: I'd drink your sweat.

HERSHER: I don't know. I'm OK with it.

KWONG: Yeah.

BRUMFIEL: You're OK with it?

KWONG: Would you?

HERSHER: Yeah, I'm cool with it.

KWONG: You wouldn't drink our sweat?

BRUMFIEL: Absolutely not, Emily. What is wrong (laughter) with you?

KWONG: At least it's not blood popsicles. I have a rapid-fire sweat-fact round. What else about sweat have you found? What stones have you...

HERSHER: Pick me.

KWONG: ...Turned up?

HERSHER: Pick me.

KWONG: Pick you, pick you.

HERSHER: Pick me.

KWONG: Pick you - Rebecca Hersher. Go.

HERSHER: OK. This is my sweat but also nonsweat fact.

KWONG: OK.

HERSHER: It's about hippos. So hippos - you know, they have that glistening skin, right? So you might think, like, hippos are really sweaty. They look - I think they look sweaty.

KWONG: Yeah.

HERSHER: They are not sweaty, though. They're covered in mucus.

KWONG: Oh, gross.

HERSHER: That's reddish mucus that protects their skin. It's very important, Emily. Don't be grossed out. It's just part of life. But it's called - because it's reddish and it looks like sweat, it is called blood sweat.

KWONG: That is metal of them. That's so - I had no idea.

HERSHER: Yeah. You're welcome.

KWONG: They do. They kind of glow.

HERSHER: With blood sweat.

GREENFIELDBOYCE: Well, Geoff, as you learned, the line between, you know, sweat and blood - it's a pretty thin line.

BRUMFIEL: Yes. Nice transition there, Nell. Yeah, so my fun sweat fact is that there are a lot of insects that actually rely on sweat and tears. And the reason is you need sodium, if you're an insect, to make eggs - if you're a female, in particular. But flowers - nectar doesn't have sodium. And so one strategy...

KWONG: So they're drinking...

BRUMFIEL: ...Insects have evolved...

KWONG: ...Our sodium.

BRUMFIEL: Yep. Sweat bees - there's a whole bunch of different sweat bees all over the world. Some butterflies and moths do it, too. And there's a theory, which is what Nell was alluding to, that mosquitoes were actually once sweat feeders until they figured out there was a much more nutritious, salty fluid right next door. And so they figured out how to drink our blood.

KWONG: Nell, sweat fact?

GREENFIELDBOYCE: The one I learned recently that I thought was interesting is just that we have two different kinds of sweat. So, you know, the focus is always on the sort of salty, liquidy sweat, which is what Geoff was just saying, you know, insects want to drink from us. But there's also a completely different kind of sweat that is...

KWONG: Yeah.

GREENFIELDBOYCE: ...Like, more waxy and like, more smelly.

KWONG: Do you know under what circumstance we produce waxy sweat?

GREENFIELDBOYCE: These come from a different kind of gland - and which is more likely to be found, like, in the armpits, in the groin. And so, like, some of the smell you associate with sweat is actually coming from that aspect of sweat.

KWONG: Our bodies are kind of miraculous. It's making me look back on my pubescence, which was a very sweaty time, with a bit more fondness.

BRUMFIEL: (Laughter).

KWONG: I want to close out with a bit of art. Rebecca Hersher, you got so into this, you wrote a poem about sweat after your visit to the zoo. Yeah?

HERSHER: I just want to be totally clear. It is not because I was so into it. It was because I was at a loss for how to make this not boring or sad.

BRUMFIEL: What?

HERSHER: I wanted to make it fun, you know? I wanted to make it fun.

KWONG: Well, cool. Let's hear some of it.

HERSHER: (Reading) Lots of animals pant - way more than just dogs - badgers and deer, cows, even frogs. And birds, like ravens, believe it or not.

(SOUNDBITE OF RAVEN SQWAKING)

HERSHER: (Reading) Hot, hot, hot. So check your vanity. Sweating's part of humanity. We're the moistest of creatures. Of that be proud. And the next time you're in a big, sweaty crowd, don't give into disgust, self-hate or frustration. Instead, just give thanks for your perspiration. Be impressed by your sweat, how it glistens and oozes. Rebecca Hersher, NPR News-zes.

(APPLAUSE)

KWONG: Yes. The bard of the Science Desk.

GREENFIELDBOYCE: Strong work, Hersher. Strong work.

HERSHER: Thank you very much. Thank you very much.

KWONG: Rebecca Hersher, Geoff Brumfiel and Nell Greenfieldboyce, thanks for being our sweats-perts today.

HERSHER: You're welcome.

GREENFIELDBOYCE: No sweat, Emily.

BRUMFIEL: Yeah, no sweat. No sweat. Nice. Nice, there, Nell.

(SOUNDBITE OF MUSIC)

KWONG: This episode was produced by Chloee Weiner and edited by Gabriel Spitzer. Rachel Carlson checked the facts. Stacey Abbott was the audio engineer. Special thanks to Pien Huang and Joe Palca on the Science Desk, who also contributed reporting for the sweat series, which you can listen to at npr.org. Gisele Grayson is our senior supervising editor. Beth Donovan is our senior director. And Anya Grundmann is our senior vice president of programming. I'm Emily Kwong. Thank you for listening to SHORT WAVE. Stay cool out there, and we'll see you tomorrow.

(SOUNDBITE OF MUSIC)

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