Short Wave - Sweat: A Human Superpower

Episode Date: July 27, 2021

Sweating is critical to helping humans avoid overheating, and it's different than how most animals cool down. Sarah Everts wanted to understand more about how humans came to sweat like we do, and wrote a book called The Joy of Sweat - which she talked about with Rhitu for this episode.Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. It's July, and here in Washington, D.C., that means hot, sweaty, sticky days. Sarah Edwards hears complaints about sweaty summers a lot. She's the author of the new book, The Joy of Sweat. I've always kind of worried that I might sweat a little bit too much or sweat more than average. And, you know, I think that that's something that a lot of people feel. Uh-huh, me too. Right? And as a science journalist, I just kind of thought, well, hey, I can learn more about

this thing that we all do and, you know, perhaps find a little serenity in it. As Sarah dug into the fascinating science of sweat, she learned that it's an evolutionary marvel, a highly efficient way to prevent our bodies from overheating. We effectively dispatch water to our skin, and as it evaporates, it whisks heat away from our bodies. And in order to do that, it kind of is most efficient on a naked surface. And lo and behold, we are the naked ape. Compare that to how furry mammals cool down, like dogs or chimps. They pant. And so they stick out their tongue and evaporate saliva off their most naked part, which is their tongue. But instead of relying on like a very small amount of real estate,

we have our whole body off of which we can evaporate liquid. Sweating allowed our species to survive and thrive. It allowed us to adapt to very hot places, to run long distances without overheating, which enabled our ancestors to chase and catch prey because the prey would tire out faster. And so it's actually this incredible kind of superpower that we have. And anyone who's embarrassed or grossed out by sweat, Sarah says, Think again, it could have been so much worse. So like vultures will poop on their legs.

It's very liquidy to evaporate that liquid off. Seals will urinate on themselves to also evaporatively cool their bodies, right? And so, you know, when you know what could have been, what evolution may have bequeathed us, sweat is arguably a million times better, right? Like, at least we're all just sweating, not peeing, pooping, and licking ourselves. to coolness. Today we explore this distinctly human function. Sarah Everts explains how it works and why we should rejoice in our sweat. I'm Ritu Chateji. You're listening to Shortwave, the Daily Science podcast from NPR. So Sarah, in your book, The Joy of Sweat, you write that to

sweat is human. So how much someone sweats is sort of a mix of their genetics and also where they grew up, right? Yeah, so it's kind of interesting because these glands, they're called Ekrine glands, that's what scientists call them. You're born with all the equine glands that you'll ever have, but when you're, in your toddler years is when they all fully become active. And so in those very early years of your life, your body is kind of learning about the climate that you're in. And researchers are trying to figure out, you know, how much of the environment in which you spent your early years is, you know, ultimately going to affect how much you sweat as an adult. And so that's like the nurture part. But of course, there's also a nature part.

You know, some people are just sweatier than others and some families are. And, you know, perhaps you have, you know, more sweat glands than average. Most people have between two and five million. I got mine counted. I have three million. Probably TMI. And, you know, there's also the flow rate, right? So, you know, some people, you know, are very efficient with their sweating and some, you know, the floodgates just open right up. And so that's also possibly related to genetics, but also possibly related to, you know, acclimatization. And your body learning on the go. I mean, athletes do this, right? Like I'm preparing for, you know, the Olympics in a really hot place.

They will try to train in very similar conditions so that their bodies learn to cool them down. efficiently in that kind of environment. And as you write in the book that despite Sweat's main role as a way to cool our bodies, sweat itself, the contents of it is so much more than water, right? The salt for one. Oh, yeah. So this was the thing that really blew my mind. So, you know, when you think about sweat, it took me a long time until I was writing this

book to be like, where is it really coming from? And it's effectively the liquidy parts of blood, minus as the big stuff like red blood cells and platelets and immune cells. And so, you know, if you open up a body, you're very wet inside, right? You have this thing called interstitial fluid that's keeping all your organs damp and moist, right? And that liquid is sourced from blood. And when your body gets the cool-down directive, then your sweat glands source sweat from that interstitial fluid. And so literally anything that's in your body, blood that's small can percolate out. So, you know, evidence of my morning coffee comes out

in my sweat. When I have a drink of, when gin and tonic on a hot day, definitely the alcohol comes out, evidence of the food we eat, evidence of our health, or even how we're exercising. Yeah. And a story that you write about in the book about the, I think was it a South African nurse who sweat turned red. Yeah, so, oh, to be this woman. So she was a nurse and wore a white uniform and noticed that her sweat was red. And, you know, this is a very strange situation, right? I would freak out.

Yeah, I would freak out. So she was really insecure about it and went to a dermatologist who got really interested. But they could not, for the longest time, figure out what, was going on because she was in her 20s. She was perfectly healthy. You know, they checked her for everything. Anyway, this one day she comes to the clinic for a follow-up appointment. And one of the doctors notices her fingers are kind of stained, like a reddish brown color. And it turns out she had had a pre-appointment snack. And it was this corn chip called spicy tomato. She was very, fond of these chips. Like she was eating multiple bags a date, like very fond. Like the dermatologist

called it a fetish. And it turns out, you know, they analyzed her sweat for, you know, the same colorance and dyes as the chips and, you know, got a match. And so effectively, once she dialed down her predilection for these particular chips, her red sweat disappeared. But, you know, other people have turned their sweat all sorts of colors for all sorts of reasons. It's kind of like a funny little corner of the medical literature called Chromehydrosis, chrome like colored and hydrosis for sweat. So fascinating. So about the other components that sort of leak out into sweat, do they have any role? So what's coming out of your sweat pores? The like entire medical role for your biological role is to keep you cool. But in the process,

your body also dispatches some proteins that do crowd control for the microbiome of your skin, right? So helping the helpful bacteria thrive and, you know, trying to keep pathogens at bay. But most of the stuff that comes out in this watery sweat called Ekrine sweat is just what happens to be, you know, flowing around your body. Of course, there is another kind of sweat, the stuff that makes you really stinky. That's the sweat that comes out in your armpits. It's actually an entirely different kind of sweat gland. It's called the apricline gland.

And it gets active at puberty, right? As we all know, or as many of us know. And that sweat is not like salt water at all. It's kind of like waxy, a little bit similar to earwax, but a lot more minute. And the bacteria living in your armpits, eat that sweat. and metabolize it as the science target goes and effectively poop out what is the body odor that comes from your armpit. And so does body odor change depending on kind of the content of your sweat and the mix of bacteria that are metabolizing the sweat? Exactly. And so we all have a unique

body odor print, right? We all have our own smell. Yeah. And, you know, that is effectively the mix of waxy molecules coming out of those apricrine glands, plus the unique to you ecosystem of bacteria living in your armpit. And so that combination is what gives you your unique odor print and mine and allows dogs, for example, to track humans based on, you know, having sniffed something that they've worn. Right. Now, you know, as essential as sweat is to our physiology, You're right that it is relatively poorly understood by scientists. Why is that? And what are the things we still don't understand or know about sweating? Right. So, you know, scientists have studied sweat. So I don't want to like give that impression. But if you just look at the scientific literature, other bodily fluids get so much more attention. And some of the really interesting areas are, you know, the evolution of sweat glands and how. how we actually came to be to have evolved one of the most efficient ways to cool down in the animal

kingdom. We don't even know how many genes are involved in sweating. And a lot of other really fabulous research is still going on, trying to, for example, do the forensics of science, like monitoring what is coming out when we sweat and monitoring what are the chemical residues in a fingerprint because like a fingerprint is just a sweatprint. And forensic researchers are now able to learn all about your biological identity from the actual chemicals left behind in the fingerprint. If you can analyze the chemicals of that fingerprint and find out, wow, that person was, you know, drinking alcohol or, hmm, that person actually has cancer. All sorts of very private information is being, you know, left behind in the drips we leave on our yoga mats, but also

literally on everything that we touch. Sarah Everts is a science journalist and the author of the new book, The Joy of Sweat. This episode was produced by Rebecca Ramirez, edited by Jaselle Grayson and fact-checked by Indy Kera. Josh Newell was the audio engineer. I'm Reed Dutateji. Thanks for listening to Shortwave, the Daily Science podcast from NPR. Good question.

That's a really good question. It's a great question. This is free therapy. Thank you for asking me that. God, that's such a good question. That's an interesting question. But what Fresh Air interviews are really about are the interesting answers. Listen and subscribe to Fresh Air from W. H.Y.Y and NPR.