When most bodies get hot, sweat starts pouring out. Why? In this episode, we'll hop in the Amazing Truck of Minimization (ATOM) to see how sweat glands work from the inside out, take a peek back in time to figure out how we evolved to be so sweaty, and we'll find out if there are any other animals as sweaty as we are. All that plus a brand new mystery sound!

Audio Transcript

Download transcript (PDF)

CREW: You're listening to Brains On!, where we're serious about being curious.

CREW: Brains On! is supported in part by a grant from the National Science Foundation.


MOLLY BLOOM: I am so glad we got to visit the bookstore together, Violet.

VIOLET: Yeah, I love books. And I finally got my very own copy of your books, Molly.

MOLLY BLOOM: Oh, you mean Earth Friend Forever and Road Trip Earth? Yay! I'll be sure to tell Sanden and Marc that you-- oh, wait-- is that Gungador down the street coming out of a dance studio?

VIOLET: It totally is. Uh, what is he wearing?

MOLLY BLOOM: Gungador! Gungador, wait up!

GUNGADOR: Huh? Oh! It Molly and friend. Hello! Gungador has just become champion of Zumba!

VIOLET: Wow. Hey, um, what's that you're wearing, Gungador?

GUNGADOR: This? Oh, this is Gungador's new invention-- the better sweater sweater. Wear this sweater when exercising.

MOLLY BLOOM: Um, but won't that make you extra hot and sweaty?

GUNGADOR: Correct. Sweat more. Become sweat master like Gungador-- most powerful sweat in the world. And best part is better sweater sweater saves all your sweat. You can wring sweater out and use later.

VIOLET: What will you use all that sweat for?

GUNGADOR: For so many things-- water, flowers, wash between toes, give cool hairstyle to dog. Come here. Give Gungador a big sweaty hug. It good for you.

VIOLET: So what now?

MOLLY BLOOM: Oh, I'm so wet.

GUNGADOR: Yes! Feel the power of sweat. Sweat keeps you cool-- cool like Gungador. Good to see you, friends. Gungador needs snack now. Goodbye.



VIOLET: You know what? Now that I'm not hugging Gungador, I can feel a breeze. I do feel cooler.

MOLLY BLOOM: Yeah. Me too. The Gungador sweat is evaporating into the air, and it's taking some of our body heat with it. I guess that's what happens when humans sweat too.

VIOLET: Are all humans and Gungadors the only animals that sweat? Does sweat do anything else besides cool us off?

MOLLY BLOOM: Great questions. Let's find out, and we can tell Gungador all about it later.


You are listening to Brains On! From APM Studios. I'm Molly Bloom. And my co-host today is Violet from Rock Hill, South Carolina. Hi, Violet.


MOLLY BLOOM: Today, we're all about sweat, sweet sweat.

VIOLET: Yeah. I want to know what sweat actually is and why we get sweaty.

MOLLY BLOOM: Our listeners want to know too. Check it out.

KENZIE: Hi, my name is Kenzie. I live in Minneapolis, Minnesota. And my question is, "Where does sweat come from? And why is it so stinky?"

DONOVAN: My name is Donovan from Elizabethtown, Pennsylvania. My question is, "Why do we sweat when we're hot?"

ELLIOTT: My name is Elliott from Atlanta, Georgia. My question is, "Why do we sweat? And how does it work?"

VANCE: My name is Vance from Sioux Falls, South Dakota. My question is, "What causes us to sweat? And how does it help us cool down?" I got this because I'm in Tae Kwon Do and I get very sweaty.

JEN: Hi, I'm Jen from Austin, Texas. And my question is, "How does sweat fall?"

LILA: My name is Lila. I'm an 11 year old from Auckland, New Zealand. My question is, "Why do we sweat? How does our body produce sweat?"

MOLLY BLOOM: Such excellent questions. Violet, are you a person who gets sweaty?

VIOLET: Yes. Definitely.

MOLLY BLOOM: Yeah. And I imagine where you live in South Carolina it's probably hot sometimes.


MOLLY BLOOM: Is it-- does it get humid too?

VIOLET: Sometimes.

MOLLY BLOOM: So, does your sweat smell to you?

VIOLET: Not really. Not to me.

MOLLY BLOOM: Do other people's sweat smell to you?

VIOLET: My brothers, yes.

MOLLY BLOOM: [LAUGHS] How old is your brother?

VIOLET: Seven.

MOLLY BLOOM: Hmm. Say, "Please take a bath. It's time."


So what are some of your favorite ways to cool down when you're really hot and sweaty?

VIOLET: I like to cool down with water balloons if we have any. I also like to play with the hose in a pool. It's really like-- I like to cool down with water.

MOLLY BLOOM: Very good ideas. Well, I know the perfect way to get some answers to our sweat questions. Come with me to the Brains On! Inventorium where we keep all the cool stuff that we use to explore the world.


VIOLET: Whoa! Look at all this stuff! That's the Explorer over there--


--the door to the Hall of Slides--


- --and there's Elevator!


Hey, what's that shiny rock in the display case?

MYSTERIOUS VOICE: That's a crystal.

MOLLY BLOOM: And over here-- ta-da-- the ATOM-- the Amazing Truck of Minimization-- A-T-O-M. This sweet machine here will let us travel inside the human body to explore sweatiness from the inside-out. Want to go for a ride?

VIOLET: Heck, yeah.

MOLLY BLOOM: Perfect. Oh, there's Marc. Hey, Marc, you got a minute to help me and Violet?

MARC SANCHEZ: Oh, hey, Molly. Hi, Violet. I was working on this Triple Decker Sandwich Fabricator, but I was just about to take a break. The lettuce tube on this thing keeps malfunctioning.


MOLLY BLOOM: Do you want to be our host?

MARC SANCHEZ: Oh, wow! I've been practicing for this. You want to hear? (CLEARS THROAT)

(IN A DEEP VOICE) You're listening to Brains On! I'm Molly Bloom.

Pretty good, right?

MOLLY BLOOM: Oh, hang on. Sorry, Marc-- not Brains On! host-- Violet and I want to check out how sweat works, So we're going to take the ATOM for a spin, and we need someone sweaty as a host.

MARC SANCHEZ: Oh! Cool, cool, cool, cool. No problem. [CHUCKLES] I definitely worked up a sweat trying to attach the mayonnaise and mustard tanks, so I'm good to go.

MOLLY BLOOM: OK, Marc, you just sit in this chair and relax. Violet, let's fire up the ATOM. You're on the copilot controls right here next to me.


VIOLET: Um, Molly, there's only one control over here, and it's a big blue button that says, "Shrink."

MOLLY BLOOM: Yep. Hit it, violet.



Now that we're tiny, you just got a fly into one of Marc's pores so we can see his insides.

MARC SANCHEZ: Yuck. This part always tickles.

MOLLY BLOOM: OK. Now that we're in Marc's body, I'll let the ATOM's autopilot take over.


TINA: Welcome to ATOM. I'm your guide, Tina. Please state your destination.

VIOLET: Take us to the sweat, please.

TINA: Fasten your seatbelts. Sweatseeker, engage.

MOLLY BLOOM: Check out the view screen, Violet. I think we're in Marc's bloodstream. You can see tons of red blood cells. They look like inner tubes.

VIOLET: I guess we're headed up to the heart. I can hear the heartbeats from here.


MOLLY BLOOM: Ah, I always knew Marc was a big-hearted guy. Hmm, this blood vessel we're in now looks a lot smaller than the one we were in before. We must be in one of the little veins close to the surface of the skin.

VIOLET: Whoa! I don't see blood cells anymore. It looks like we've taken a detour out of the bloodstream and into layers of something. Hey, Tina, where are we?

TINA: We are in the epidermis, the outer layer of skin. That's the part of human skin that contains sweat glands.

MOLLY BLOOM: Oh, look up ahead there. I think that's a sweat gland. It says here on the ATOM's screen that sweat glands are a part of the body's sympathetic nervous system which is made up of organs connected to the brain by nerves that pass information along the spinal cord.

VIOLET: Wait-- sweat glands are organs like kidneys and lungs?

TINA: Correct. An organ is any group of tissues in your body that has a specific job. Your kidneys help filter out unwanted material from your body. Your lungs take in oxygen. And your sweat glands make sweat.

MOLLY BLOOM: ATOM says that humans have between two and four million sweat glands all over their bodies with lots of those on the palms of the hands and soles of the feet and more spread out over the rest of the whole body.

VIOLET: And sweat is basically just salty water, right? I know when I've gotten sweaty, I taste salt on my skin.

TINA: Correct again. Sweat is water and salt.

VIOLET: Wait-- but why do we get stinky when we sweat? Salt water doesn't smell like anything, and sweaty people definitely smell like something.

TINA: Enhancing visuals on screen. Zooming in on eccrine glands.

MOLLY BLOOM: Whoa! The sweat gland is also making some kind of cloudy goop.

TINA: Eccrine glands are a specific type of sweat gland. You also have apocrine sweat glands which make sweat without the goop. That cloudy liquid is proteins and fatty acids. And those happen to be molecules that tiny things called bacteria find delicious. And you are covered with these pretty harmless bacteria.

MOLLY BLOOM: Oh, that must be the bacteria grazing on the sweat goop now.

VIOLET: Wait! Do bacteria eat sweat and poop out stinky smells?

TINA: Sort of. Bacteria break down those proteins and fatty acids into other molecules, which can have a smell, especially after a person goes through puberty and their body changes. That makes them create more hormones, and those can lead to smellier smells from sweat.

MOLLY BLOOM: Ha! That's gross and awesome. Thanks, Tina. I think we've probably been inside Marc long enough. Can you take us back to the Inventorium and re-enlarge, please?

TINA: Can do. Seatbelt still on? OK. Here we go.


MARC SANCHEZ: Hey! You're back. How was it? Was I sweaty enough?

MOLLY BLOOM: You were perfect.

VIOLET: Yeah, thanks, Marc.

MARC SANCHEZ: My sweat is your sweat anytime. Violet, can you hand me that wrench? I need to get back to work on this lettuce tube.


CHILD: (SINGING) Brains on, on, on.

VIOLET: Hey, Molly, what's in these jars over here?

MOLLY BLOOM: That's some of our collection of mystery sounds. Do you want to open one?

VIOLET: Hmm. I'll try this one.


CHILD: (WHISPERING) Mystery sound.

MOLLY BLOOM: OK. Let me unscrew the cap. OK. Here it is.


OK, Violet, what is your guess?

VIOLET: I have no idea.

MOLLY BLOOM: [LAUGHS] You want to hear it again?




VIOLET: It kind of sounds like someone crushing a can, maybe.

MOLLY BLOOM: Ooh, excellent guess. We're going to give you one more chance to guess and hear the answer after the credits, so stick with us.


We absolutely love seeing your drawings. If you're feeling inspired, may we suggest drawing Gungador's exercise class or maybe the ATOM, seeing how sweaty Marc actually is? Send those drawings to us at brainson.org/contact. And while you're there, you can send us mystery sounds, high-fives, and questions.

CREW: Like this one--

JASPER KAVANAGH: Hi, my name is Jasper Kavanagh. I am nine years old and from Chapel Hill. My question is, "How does the Earth support really heavy buildings like the Empire State Building?"

MOLLY BLOOM: You can hear the answer by listening to our Moment of Um! podcast. It's a daily dose of facts and fun every weekday. You can find it wherever you listen to Brains On! Just search for Moment of Um! And be sure to stick around for the end of this episode to hear the latest group to join the Brain's Honor Roll.

VIOLET: So keep listening!


You're listening to Brains On! I'm Violet.

MOLLY BLOOM: And I'm Molly. And we just came from exploring Marc's sweat glands. It was great.

VIOLET: I'm still thinking about how many sweat glands we have-- up to four million all over our skin. That's so many. Why do we have so many places we can sweat from? Are we the only animals who sweat? I have so many more questions.

MOLLY BLOOM: I think I know someone who can answer some of them. Come with me. Her office is right down the hall.


ANNA GOLDFIELD: Come on in. Oh, hey, Molly.

MOLLY BLOOM: Hi, Anna. Violet, this is Anna Goldfield who knows all kinds of stuff about science and humans. Anna, this is Violet.

ANNA GOLDFIELD: Nice to meet you, Violet. What can I do for you?

VIOLET: I have some questions about sweat. Why do we sweat all over our bodies? Have humans always been sweaty?

ANNA GOLDFIELD: Ooh, great questions. And I have something in one of my desk drawers here that will help me answer them. Hang on.


Where did I put them? Notebook, keys, clown horn [HONK], ah two pairs of Chronovison goggles-- virtual reality goggles that let you see into the past. Go ahead. Put them on. I've got the controller right here. Check this out.



ANNA GOLDFIELD: You're looking at the African savanna about a million years ago. Tell me what you see.

VIOLET: I see a big, open, grassy plain. It's daytime. And the sun is really shining. There are a few trees with shade underneath but not many. It must be super hot.

ANNA GOLDFIELD: OK. I'm going to zoom in a bit. How about now?

MOLLY BLOOM: Ooh, I see a few lions napping under a tree. Oh, they're all sleepy and floppy. One big male lion just yawned. Ooh, those are some serious teeth.

ANNA GOLDFIELD: Sure are. And some of our early ancestors shared this landscape with big dangerous predators like these lions. Now, lions usually hunt at night when it's cooler. Plus, they have really good night vision.

So if you were, say, our early ancestor Homo erectus bopping around Africa around 600,000 years ago and you didn't have that feline night vision, you'd probably want to do your hunting and gathering when big predators were too sleepy to hunt you.

VIOLET: So during the day-- but wouldn't it be too hot? I've seen museum exhibits of some of our early human relatives. And they were pretty hairy, almost like a chimpanzee. It would be like hanging out in the sun with a sweater on.

ANNA GOLDFIELD: Exactly. And chimpanzees like shady forests and don't spend a lot of time in direct sunlight. They do have sweat glands, and they sweat a bit, but they mostly pant to keep themselves cool like dogs and other mammals.

The way sweat works is that, as it evaporates, it takes some body heat with it, bringing down the temperature of our skin. Chimps are just too hairy for sweating to work well for them.

MOLLY BLOOM: So what happened?

ANNA GOLDFIELD: Evolution, baby. Gradual change over generations in response to environmental conditions. Scientists think that this is right around the time when our ancestors gradually adapted to being able to tolerate being much more active in the heat and sunlight. So two big things happened. Over time, their bodies started making more and more sweat glands all over the body, and body hair got thinner.

VIOLET: Don't you mean we lost it?

ANNA GOLDFIELD: No. Cool fact alert-- all of us humans actually have about the same amount of body hair as your average chimp. But chimp hair is much thicker and coarser. And ours is mostly very thin and downy soft.

VIOLET: Wow. I didn't know the thickness changed but the amount didn't. I have as much hair as a chimp? That's wild.

MOLLY BLOOM: And it's cool to think about some of our early sweaty ancestors out hunting on the grasslands. Thanks, Anna.

ANNA GOLDFIELD: My pleasure. Now, if you'll excuse me, I'm going to use my Chronovison goggles to watch some baby dinosaurs hatching. Later!


CREW: (SINGING) B-- b-- b-- b-- b-- b-- b-- b-- b-- b-- b-- brains on!

MOLLY BLOOM: You know, Violet, human sweat is pretty special. But we're not the only animal to do it. Time for a little game of "Sweat or No Sweat." I'm going to name an animal, and you tell me if it's sweats or not. Are you ready?

VIOLET: I think so.



VIOLET: No sweat--


VIOLET: --because they're in the water.

MOLLY BLOOM: Exactly. Yes. So since fish are always wet, they can't sweat. Good work. All right. Next animal-- horses.


VIOLET: Sweat.

MOLLY BLOOM: Correct again. In fact horse sweat has a special substance in it called latherin, which is sort of like soap. And sometimes it can make a sweaty horse look a little foamy. Have you seen that?


MOLLY BLOOM: I haven't either. OK.

VIOLET: It sounds funny.

MOLLY BLOOM: It does sound funny. All right. Next animal-- pigs--


--sweat or no sweat?

VIOLET: No sweat--

MOLLY BLOOM: Correct again. Oh my gosh. You're a sweat expert.

VIOLET: [LAUGHS] --because they--

MOLLY BLOOM: Yeah, tell me.

VIOLET: --play around in the mud.

MOLLY BLOOM: Exactly. Oh my gosh. You know so much. Yes. So when they roll around in the wet mud, that mud evaporates and cools them like sweat does. So have you ever heard the phrase, "sweating like a pig?" Have you heard people say that?


MOLLY BLOOM: Yeah, so some people say, like, oh my gosh, I'm sweating like a pig. And when they're saying that, they're not actually talking about pigs. But they're talking about making iron or smelting iron because iron smelters would pour hot liquid iron into shapes that kind of looked like a pig with piglets. So they called it a pig iron. When it cooled, beads of water would form on it and it looked like sweat.

VIOLET: Oh, that's cool.

MOLLY BLOOM: So you're really sweating like an iron smelter instead of a pig.


MOLLY BLOOM: All right. Next animal-- vultures

VIOLET: Ooh, no sweat.

MOLLY BLOOM: Correct again. Incredible. They do pee on their own legs, though, which scientists thinks helps them to cool off on a hot day.

VIOLET: But won't that make you warmer?

MOLLY BLOOM: That's a great question. Maybe for a second but then maybe it evaporates and then it makes you feel cooler?

VIOLET: Oh, yeah.


VIOLET: And it also gets colder the higher you go in the air, right?

MOLLY BLOOM: Yes. Good point. Very good point. So, yes-- so we don't recommend trying this one at home, everybody.


MOLLY BLOOM: All right. Next animal is hippos-- sweat or no sweat?

VIOLET: No sweat.

MOLLY BLOOM: This one is actually sweat. They do sweat.


MOLLY BLOOM: Well, OK, let's say sort of. And so I'd say you're half right. So hippos make a really unique substance sometimes called hippo sweat, appropriately.


MOLLY BLOOM: But it's not like our sweat. It's actually kind of reddish, almost like blood. And it's super cool because it helps kill bacteria, keeping their skin moist and it even acts like a sunscreen.

VIOLET: That's funny.

MOLLY BLOOM: Yeah. So I think hippo sweat may be the next big thing in skincare. It sounds pretty cool.

VIOLET: Yeah. It does sound really cool.

MOLLY BLOOM: Well, you did very well. You only got half a point off this entire quiz. So I think you are definitely a sweat expert today--


MOLLY BLOOM: --or a sweatspert, shall we say?



Oh! Got to go or we'll be late. I signed up for Gungador's dance class. He's teaching aerobic polka. So, you want to come with me, Violet, and we can tell him everything we learned today about sweat?

VIOLET: I'd love to. Let's break a sweat.


We have millions of sweat glands all over our body. And we evolved that way to help us be active in hot climates during the day.

MOLLY BLOOM: Sweat keeps us cool thanks to the power of evaporation.

VIOLET: Our sweat glands are in the outer layer of our skin, the epidermis.

MOLLY BLOOM: Some of our sweat glands just make sweat and others add proteins and fatty acids, which bacteria snack on, and that's where stinky body odor comes from.

VIOLET: Humans aren't the only animals that sweat. But we are definitely one of the sweatiest species on Earth.

MOLLY BLOOM: That's it for this episode of Brains On!

VIOLET: Brains On! Is produced by Molly Bloom, Sanden Totten, Marc Sanchez, Rosie DuPont, Ruby Guthrie, and Anna Weggel.

MOLLY BLOOM: Our fellow is Anna Goldfield who wrote this episode without even breaking a sweat.

VIOLET: Brains On! is a non-profit public radio program.

MOLLY BLOOM: There are lots of ways you can support the show. You can donate, buy our books, or tell your friends about us.

VIOLET: Head to brainson.org to find the links to donate and order the books.

MOLLY BLOOM: OK. So, Violet, we have still got the mystery sound jar from the Inventorium. So do you want to take another crack at it?


MOLLY BLOOM: Here it is again.


VIOLET: I still think it's the can.

MOLLY BLOOM: Excellent. Here is the answer.

OWEN: My name's Owen. I'm from Portland, Maine. That was the sound of me crinkling a can. That sound makes me feel calm.

MOLLY BLOOM: You're correct!


MOLLY BLOOM: 100% correct. Excellent. Excellent ears.

VIOLET: That one was hard.

MOLLY BLOOM: Yeah. And you got it so really good work.

CREW: (SINGING) Brains, brains, brains.

MOLLY BLOOM: If you have a mystery sound you want to share with us, you can do that at brainson.org/contact. Everyone who sends a question, idea, mystery sound, drawing, or high-five gets added to the Brain's Honor Roll. Here's the most recent group of listeners to be added.





MOLLY BLOOM: We'll be back soon with more answers to your questions.

VIOLET: Thanks for listening.

Transcription services provided by 3Play Media.