(Timestamps from YouTube):

Dan Riley [00:00:57]:
I would love to start at the beginning with how you got interested in the subject of sweat and perspiration. There's a lot I want to get into about the, the subject itself, but for you personally, what is the background story on your own personal interest in the subject? Yeah.

Sarah Everts [00:01:15]:
Well, I like to exercise a lot, and I'm a person who's also really sweaty, so I kind of always have felt a little bit mortified by my sweat. So, you know, at any spin class or any yoga class, I am the first person to start dripping on the mat, even in the warm up. And so instead of, like, focusing on my downward dog and being zen, I'm, like, looking around to see if I'm the only one who's sweating. So, like, I always felt a little bit insecure about how quickly and how much I sweat, although I was only really sweating, you know, when I was doing exercise. But I'm also a science journalist, so I had spoken to a lot of evolutionary biologists, and I knew that sweating was actually a human superpower, that evolutionary biologists consider it one of the things that makes us unique in the animal kingdom, along with being the naked ape and having big brains. And so I figured I needed to dig in a little bit deeper to rectify this disconnect between this thing that supposedly makes us amazing as animals and this thing that we kind of all are a little bit mortified by, or many of us.

Dan Riley [00:02:28]:
I would classify myself in that category of people who are mortified by my own capacity to sweat. So I sympathize. You go into detail in your book about the fact that sweating really is a superpower, or at least has been a superpower for humans in our evolutionary history. And I would love to give you some time to really give some detail about why that is, what we know about the importance and the role of sweat in our own history.

Sarah Everts [00:02:58]:
Yeah, sure. Well, sweating, ultimately, is there to regulate our body temperature, because if we go too high, we can die of heatstroke. And death by heatstroke is a terrible way to die. Like, google it. It's very bad. Bad things happen. And so we all animals, need to find ways to cool down. And as it turns out, humans evolved the most efficient way in the entire animal kingdom for doing that.

Sarah Everts [00:03:29]:
And it's part and parcel with being the naked ape. So what happens when our body temperature rises is that we begin to sweat, right? Two to 5 million sweat glands on every human body. So the pores open, liquid comes out, and our body heat evaporates that liquid away, and that chemical process consumes heat. So, effectively, your sweat's evaporation is whisking the body heat from your body up and away into the atmosphere. And as you can imagine, having a non furry, non hairy surface is an optimal way of doing that. So if you think about other animals, such as a dog, they evaporate their body heat off of the only naked part of their body, which is their tongue. Right? That is not a lot of surface area. Even our closest evolutionary neighbors, the chimpanzees, they pant to cool off.

Sarah Everts [00:04:28]:
Instead, we use our entire surface area. And as a result, we can withstand a lot of really warm temperatures. When it's cold, we wear the fur of other animals. And when it's hot, not only can we handle the heat very well, better than most other animals, but we can also exercise in the heat. And this is really important for human evolution, because, as you can imagine, in the early days of humanity on the savannah, all of our prey and most of our predators run faster than we do. And so how do you hunt? How do you escape? Well, in terms of hunting, think about an antelope, right? Well, it can definitely sprint faster than humans, but it ultimately needs to stop and cool down by panting, usually, so that it doesn't die of heatstroke. Meanwhile, humans can exercise and cool down at the same time, and that's the trick of sweating. And it's only because we have so much surface area.

Sarah Everts [00:05:31]:
So when that antelope shoots off, we run after it. It stops to cool down. We catch up with it, forcing it to run again and again and again. Meanwhile, we're staying coolish by sweating and ultimately either dies of heat stroke or become so weakened that it's easy to kill. And so this is really how come humans are able to survive most climates on earth and why we've dominated this planet. I mean, for better or for worse.

Dan Riley [00:06:01]:
Hmm. I feel like that is such an underappreciated component of what it means to be human and an underappreciated fact of our rise to the top of the food chain. You gave some detail just now about how that process typically worked, and I wonder if it might make sense to pause and just have you re articulate in any more detail you might like to give about how that process worked for how we hunted game historically, where everyone knows, like you just said, that the big game on the savannah are all more physically, seemingly capable than people.

Sarah Everts [00:06:42]:
Are, but, well, they can sprint faster.

Dan Riley [00:06:44]:
They can sprint faster. And so the length of time that it typically takes to, for example, with an antelope or some other big game, what's the. What's the story about how that typically, because I know there are still hunter gatherers around now that I'm sure are implementing this strategy. How exactly does that story typically unfold with how we're able to successfully hunt?

Sarah Everts [00:07:06]:
Well, I mean, we can still run marathons these days, right? Humans, even in modern society, can run for hours. The fastest of us can run, you know, a marathon in 2 hours straight. Others take four, five, 6 hours of continuous running, whereas, you know, an animal must sprint away very quickly to get away from us. But it can't maintain that sprint for long, because if it does, its body heat will rise. And if that happens, every cell in its body starts to effectively melt. And all sorts of bad things happen with heatstroke. So, for example, your digestive tract, the membrane becomes weak, and all the bacteria in your gut start to invade your body. You have seizures, vomiting is involved.

Sarah Everts [00:07:56]:
It's really a terrible way to die. And so all of us constantly, all animals, mammals specifically, are trying to keep your body temperature, their body temperature in a very fixed area, right? Like in a very small window. And so, actually, right now, I don't appear to be sweating, but I am. I am sure you are sweating because our body's making these micro adjustments to our body temperature, and we only notice the sweat, the wetness, when we really exercise a lot. And that's because our body is like, oh, crap. We're not just doing a little bit of exercise. We're really going wild. And so your body gets cracking and make sure there's enough liquid on the surface of your skin so that all of it can evaporate away.

Sarah Everts [00:08:46]:
And that evaporation process is actually a lot like making a reduction, as they would say in foodie world, right? So effectively, in order to make liquid go away when you're making a reduction, you need heat. And so your body heat is actually providing the energy for the water molecules on your skin to evaporate up into the atmosphere. And so it's consuming the heat in your body. And for humans in particular, when we start to exercise heavily or go into a hot sauna, for many of us who are lighter skinned, the first thing that you notice is that your face turns red, right? And that's because all of your veins are pushing up against the skin. That's got two goals. The first goal is that all the hot blood in your interior is coming to the surface of your skin so that it can be cooled off by this sweat evaporation. Then the other reason that you turn red is because those sweat glands, they need to source something. You don't just have little bags of water next to all of those sweat glands.

Sarah Everts [00:09:59]:
Sweat glands source that liquid from your blood. That's why it's often really to rehydrate after you've sweat a lot, because otherwise your blood will get thick, right. You are losing water from your circulatory system. So that is why you turn red. And also that's why it is such an efficient way of cooling down. Because if you think about the entire human body compared to, say, what a dog uses, right, that is just this very tiny tongue. I mean, dog tongues seem pretty large and kind of gross and slobbery, but that tiny surface area is cooling down the entire beast, some of which are almost as big as small humans, right? And other animals use this thing called evaporative cooling. That's the scientific term for using the evaporation of water to cool down the body.

Sarah Everts [00:10:54]:
And so we're using sweat, which is its own bodily fluid. Animals like chimpanzees and dogs are using saliva, but other animals use literally any other bodily fluid that they have available. So seals will pee on themselves to evaporate away urine. Some birds, like vultures, will poop on their own legs, right? Because bird poops, kind of liquidy bumblebees will vomit on themselves. And so when you think about how evolution could have bequeathed us a cooling down strategy, sweat may seem gross at times, but in comparison to the rest of the animal kingdom, we're doing pretty good, right? Can you imagine being on a subway and having all the other bodily fluids being used to cool everybody down.

Dan Riley [00:11:47]:
Yeah. That would make living in New York even slightly more horrifying. Yeah, that's fascinating stuff. And the history of our ability to track down, successfully track down prey. I'm curious, in your research, if you uncovered any information as to how far, typically an antelope, for example, or other other animals that humans have historically hunted are able to sprint away before they need to rest. And what that math kind of looks like is it they run a mile and they need to rest for five minutes, and so there's enough time for us to catch up. Any idea about how that typically works?

Sarah Everts [00:12:27]:
Oh, like, the exact math. I think it would be really dependent on the runner and on the species at hand, but it is like, you know, on the order of, they can sprint for minutes and we can run for hours. Right. So if they are sprinting extremely fast, then we can catch up relatively soon, but not soon enough for them to completely cool down. Right. So it's this. We're pushing them past their ability to stay cool and effectively pushing them into heat exhaustion, making it easy for them to be killed or just actually, literally killing them.

Dan Riley [00:13:04]:
Yeah, fair enough. The. You know, a question. I have just always wondered about different people, and I think I mentioned this to you before we started talking, that there's no question in my mind, in my own family, I sweat. Am in the most sensitive to heat of anyone in my immediate nuclear family. What do we know, or what did you discover? What do you know about why it is that certain people, and I think you gave a range earlier, something between two and 5 million, why it is that certain people seem to be more prone to being able to sweat more easily than others? Is there an evolutionary reason that you uncovered as to why that would be the case for certain humans?

Sarah Everts [00:13:48]:
Yeah. So, like a lot of things, it's a mix of nature, nurture, and choices. So, in terms of, like, the nature side, you are born genetically with a certain number of sweat glands. Also, it's not just the number of sweat glands that you have. It's the rate of the sweat coming out. So some people's sweat glands really just drib and drab, and others, it's like a big flood, and there's quite a large range in humans. And you can think about it this way. If all the humans in the entire world stepped into a sauna right now, um, and got sweating at their max, and if we were all about average sweaters, it would be like the floods over Niagara falls on a summer's day, right? That's all the humans in the world sweating at full on anyway, so.

Sarah Everts [00:14:48]:
But I digress. Uh, you, genetics is like, a really important part, right? So it's like how many sweat glands you have and how fast, um, they can flood your skin with liquid. Then there's another kind of environmental factor, what we would call nurture. So when you're born, although you have sweat glands all over your body, they don't all become active until your toddler years. And so your body has a couple of years in there to figure out what kind of climate you're living in, right? So I'm sure you've had the experience of going to a really hot climate, and all the locals, those seem to be, like, not sweating at all, right? And you're just, like, pouring down because you've come from a northern climb. That's because their bodies are really attuned to that climate. Because if you think about it, although it's great to cool down, if you sweat too much so that you're dripping, you are not being very efficient with water, which is a scarce resource. And over human history has also been a scarce resource.

Sarah Everts [00:15:57]:
Right? So you want to be optimal. And those first few years of your life, body is learning where you are, like where you're living and how to be optimal about it, because for most of human history, we didn't go very far away from the place that we were born. Okay, so there's a mix of nature and nurture, both of which you can blame on your parents because they presumably were in control of your genes and also where you were in your toddler years. But there is this other thing that I mentioned called choices, right? So you can teach your body to sweat more. So sweating because it's so important for cooling down, right. A lot of athletes want to sweat more when they know that they have to compete in a place that is more hot and humid than perhaps the place where they normally train and live, right? And so, for example, in front of the or just before the Tokyo Olympics, which was, like, in a very hot, humid place, athletes were training to sweat more and sweat faster because if their body's freaking out about being overheated, it's not going to be as efficient in, you know, its delivery of whatever athletic feat that person needs to do. And so you also talk to people who work in saunas or people who exercise a lot. And the more you exercise, the more you are likely to sweat sooner and faster.

Sarah Everts [00:17:27]:
And if you work in a sauna most of the time, and there's people who do sauna dancing, it's like a pretty funny little world that I discovered. You effectively start sweating the moment you walk into the hot place, instead of it being a gradual on ramp because your body has been trained that, holy crap, when Sarah goes hard, she goes really hard. And so you can kind of adjust. You can make these kind of micro adjustments to train your body to sweat sooner and sweat faster. But mostly you are working within a range that is biologically determined by your genetics and by those first few years of your life.

Dan Riley [00:18:09]:
And when you say growing up in a certain environment, is that, you know, roughly speaking, the ages from birth to ten that, you know, to toddler to toddler.

Sarah Everts [00:18:19]:
So, like two or three.

Dan Riley [00:18:20]:
And that, that is that an epigenetic phenomenon where you are, your body is basically acclimating to where you are and adjusting your genes accordingly so that you adapt better, adapt to your environment.

Sarah Everts [00:18:31]:
Yeah. So I would probably speculate that that is the case, but scientists haven't yet made the, like, epigenetic connection. But, yes, that would make sense because effectively, your sweat glands, right, they get, you know, messages to turn on, turn off, flood, don't flood. Right. And so I would imagine that there's ways to make those genes turn on faster or. Or slower. I would assume it's epigenetic, but that science has not been done that I know of yet.

Dan Riley [00:19:03]:
Yeah, fair enough. And I think you just may have answered this, but the. And I'm sure it's complicated, but generally speaking, is it the case that people. I mean, I think you mentioned this a bit ago, that there's. I've always had, especially in the summertime, a rather extreme embarrassment about showing up to parties outside and just dumping sweat all over strangers that I've never met before. I'm here, and it's one of the more embarrassing but expected social experiences that I have between the months of July and September. But overall, is it your belief that it's actually a signal of health to be able to turn on that ability to cool your body so quickly? Or is it more complicated than that?

Sarah Everts [00:19:56]:
Yeah, I mean, of course there's complications, but honestly, we all need a perspiration. Pep talk like sweat is keeping us all alive. Thank you very much. Um, certainly there are situations where illnesses can make you sweat more. A couple of examples, folks who, you know, have a seizure. Um, there's some medications that make you sweat more. There was, in the middle ages, a sweating epidemic. They called it the english sweaty.

Sarah Everts [00:20:29]:
And people would start sweating and then die very quickly within days. Yes, there are some actual conditions where sweating is not healthy. There's also a couple of conditions where folks really, really sweat a lot. That of is a clinical condition. And effectively, about one. You know, about 15 million Americans have this. It's called hyperhidrosis. And this is a level of sweating that is quite off the charts.

Sarah Everts [00:21:07]:
So you sometimes have a problem holding a pencil because your hands are so sweaty that it just falls out. So you drop your cell phone or holding a piece of paper, it will dissolve in your hands. And that is a condition. And it's most likely related to the autonomic nervous system. The signals are to cool down or to close or that you are cooled down enough, they get messed up. There's, on the other hand, some conditions where people are born without sweat glands, and it's a genetic condition. Those folks, that's a very dangerous situation because they can very easily die of heatstroke. They can't go to warm places.

Sarah Everts [00:21:55]:
They're constantly walking around with a little spritz bottle to literally put sweat on their bodies to evaporate their heat away. So in most cases, though, sweating is super healthy. Right. It is keeping all of us alive. We just have this really funny anxiety and taboo about it that is also partly related to something that I think is kind of a fundamental human trait. Hold on with me for a second. So we love to be in control. Most of the bodily functions that we have that are slightly mortifying, we have a minute amount of control over, like, think burp or fart or if you have to pee.

Sarah Everts [00:22:48]:
Right? Like, you can control that for just a microsecond, enough to get out of the room and do what you need to do. On the other hand, sweating is this thing where we have zero control over it. Without unexpectedly, suddenly, millions of holes in our skin have opened up and liquid is coming out. That is objectively a weird thing. And so the other, the other thing thing is that although sweat glands mostly open up because of temperature signals, so when your body gets too hot, there are other signals. So stress signals cause them to open up, probably because in the height of evolution, if you're stressed, it usually means you have to run away from the tiger. And so you're probably going to need to start the cool down strategy pretty quickly. Right.

Sarah Everts [00:23:42]:
But as you know, your hands start to get sweaty, your armpits get sweaty, when you're in an interview situation for a job or when you see your big crush. Right. So there's this other uncontrollable thing related to sweating, which is against a lot of humanity's desire to have a very curated Persona, particularly now when we're all able to curate our Personas in social media, and then you go in real life to this party, and you're like a sweaty mess. Holy crap. So I think that there's, like, some fundamental things about human nature. We like to be in control, and this is a thing that is utterly out of our control. And then I think it's exacerbated by social media's perfect curation.

Dan Riley [00:24:33]:
Yeah, I think that that's certainly how I feel when I show up to those parties and I'm dripping sweat. Is that you and me both? Yeah. Yeah. And is it reasonable to say that given the potential epigenetic phenomenon that we spoke about earlier, that typically, maybe people on average, who are from northwestern Europe of ancestry are generally more likely to be super sweaters, like I probably am when placed in a warm or humid environment than, for example, people who are from, you know, from Japan, from Tokyo, or from this near the Sahara desert, for example. Is there anything to that? That one's propensity for sweat, one's likelihood of being a real sweater is typically related to your general genetic history as well?

Sarah Everts [00:25:30]:
Yeah, but I think with the whole, like, geographic question that you were alluding to, you also have to think about the issue of climate and, like, whether it is a human and humid environment or an arid environment. So you moved from Texas, correct? Right, yeah. Austin. Yeah. So that is a place which is enormously dry. Right. So if you're not wearing, you know, standard desert gear, which keeps some of the, like, hydration near you every time you evaporate. Every time you sweat, it's not just evaporating the heat off your body and achieving the goal of cooling you down, but there is, like, so little water in the air that it whisks away really fast.

Sarah Everts [00:26:16]:
And so it's actually a lot easier to cool down by sweating that way. And so you're prone to, like, sweat a lot and not even notice it because it's so arid that, like, it's easy for it to whisk away. Whereas in humid environments, if you can imagine that you've got, like, 80% humidity and you've got a sweaty person who's trying to cool down by evaporating that sweat off their face or their body, there is a back pressure because there's already a lot of water molecules in the air, and so it's harder to evaporate and to cool down by sweating. And so there's this other variable that kind of makes it tricky. So you can't just make universal rules about latitude and longitude. Right. Because you also have to consider, like, the level of humidity. And that's why people talk about this thing called wet bulb temperature.

Sarah Everts [00:27:10]:
It's connected to the point at which you. It's so humid and so hot that you stop being able to evaporate your heat away.

Dan Riley [00:27:19]:
Interesting, interesting. And that being said, do we know anything about the various ethnicities that are prone, generally speaking, to being super sweaters, whereas others are maybe in their evolutionary history, have developed not as much of a need to be sweating so frequently? Or is that not necessarily?

Sarah Everts [00:27:42]:
No, there's not been much on, like, racial differences in sweaty. And I think that's because, like, depending on where you are, it, you know, it's adjusted. I mean, even. Yeah. That's not been something that. What is genetic and interesting is connected to the other part of sweating, which we haven't talked about, which is the stink, because we have two kinds of sweat glands. And most of the time, we're either mortified and anxious by the fact that we're, like, literally dripping wet or because we're stinky. But what's really interesting is that the liquid that comes out of your body to cool you down, like the majority of your sweat glands, that sweat isn't particularly smelly unless you've had a hard night of hummus or alcohol.

Sarah Everts [00:28:33]:
And that's because it's in your blood system. Your body's trying to deal with that. And so when you're collecting water from your blood to move out, if you've had a hard night of hummus or a hard night of drinking, you smell like those sorts of things. But that's not the bo that we're talking about. Right. So in teenage years, you get an activation of a second kind of sweat gland. And it's the difference between what's called an eccrine sweat gland and an apricrine sweat gland. Eccrine is the one that's, like the salty liquid that's just kind of filtered blood, whereas apocrine glands grow anywhere where you grow hair at puberty.

Sarah Everts [00:29:17]:
And that sweat is not liquidy at all. It's more like earwax. And when that comes out, it also doesn't have much of an odor. But the bacteria living in your armpits. Right. We coexist with bacteria everywhere on our skin, in our intestines. Well, it turns out that the bacteria living in your armpits really like that waxy sweat. And when it comes out, they eat it, and they metabolize it into stinky odors that give humans their kind of, like, signature smell.

Sarah Everts [00:29:53]:
And so it's kind of a funny thing that this thing that is a little bit mortifying and which has spawned an $80 billion deodorant in antiperspirant industry is, you know, actually, you know, at fault. It's microbes that are at fault, not. Not actually humans.

Dan Riley [00:30:10]:
Yeah.

Sarah Everts [00:30:11]:
So, yeah, there's. There's that side, too.

Dan Riley [00:30:14]:
I mean, I've heard you in other interviews talk about the role of, historically, the advertising industry, specifically, I think, to America of persuading Americans to be, I think initially it was women, and then pivoted over to men to be interested in concealing some of these odors or making oneself smell significantly better. And I would love to give you an opportunity. You're welcome to speak to that in any detail you would like. But I'm also curious about. But it's no mystery to anyone who has lived in a cosmopolitan city that it's clear that different cultures have different views on body odor in general. And we clearly are deodorant obsessed and antiperspirant obsessed in America. But I'd love to give you an opportunity to talk about that phenomenon as well and as any, in as much detail as you would like to, too.

Sarah Everts [00:31:08]:
Yeah. What I'm looking for right now is I have this, like, amazing quote. Should have gotten it ahead of time. Yeah. There we are. Okay, so you were just asking me about, like, human history and how we, you know, how humans connect with our body odor. And certainly, for most of human history, we have relied on two things. Either perfume to control our body odor, or we've used soap and water.

Sarah Everts [00:31:40]:
But we have worried about the way that we smell for a very long time. I love using this as an example. Back in the roman era, there was a poet named Catullus, and he had a buddy named Rufus. And this is a letter from Catullus to Rufus. It says, wonder not Rufus, why none of the opposite sex wishes to place her dainty thighs beneath you, not even if you undermine her virtue with gifts of choice, silk or the enticement of a pellucid gem. You're being hurt by an ugly rumor which asserts that beneath your armpits dwells a ferocious goat. This they fear and no wonder, for it's a right rank beast that no pretty girl will go to bed with. So either get rid of this painful affront to the nostrils or cease to wonder why the ladies flee.

Sarah Everts [00:32:31]:
So, like, we have been worried about RBO for some time. Right. But, yeah, most of human history, we were just, like, slathering on a ton of perfume, or we were washing, or we weren't doing either, which was like the Middle Ages, when we were worried that the plague was transmitted by washing. But this was pretty much humanity until about the turn of the 20th century, when people started to. Well, in the late 18 hundreds, people discovered antiseptics. And as you can imagine, but if bacteria are eating your armpit sweat and turning it into stinky odors, if you kill them with antiseptics, then you're effectively going to stop that odor production. And so most deodorants are just antiseptics for your armpits with a little perfume added. And most antiperspirants actually do two things.

Sarah Everts [00:33:34]:
It solves both the smell problem and the wetness problem. And the way that that works is you use some aluminum based products, and it's only aluminum that works, and they plug your pores, effectively cutting off the food buffet to those bacteria that would eat your sweat and then make stinky odors as a consequence. And it was at the dawn of the 20th century that these sorts of products were being introduced. But because it was also the victorian era, at least in our part of the world, people were so mortified by discussion of armpits writ large or bodily fluids that nobody wanted to buy these products. It was too embarrassing to talk about, and it was really hard to get them sold until this very famous J. Walter Thompson copywriter. His name was James Young, and he was working with a company that sold an antiperspirant called Odor. Oh, no.

Sarah Everts [00:34:40]:
And it was a product that had been invented from a surgeon who was from Cincinnati. And he was worried that his hands were too sweaty in the operating room, and that if he was operating in the middle of summer, that, like, something bad could happen. Maybe he'd, like, drop the knife or it would slip. And so he had invented this thing that stopped his hands from sweating. Meanwhile, his teenage daughter was like, great for your hands. What about for your pits? And launched this. This. This company called Odor Au no.

Sarah Everts [00:35:14]:
That had very poor success. It was, like, not doing well at all until this guy came up with this idea that we shouldn't be advertising antiperspirants and deodorants as a cure for stink. Right? Because most people didn't think they had a problem because they'd been washing and using perfume for time immortal. Instead, they said, oh, yeah, you can do those things that stop your stink. But is it really working? Actually, it's not worse than that. Your armpit smell, your body odor is interfering with you finding love. And initially they focused on women trying to find a man. And they had taglines like, beautiful but dumb.

Sarah Everts [00:36:06]:
She has never learnt the lasting rule of getting a date and a man. And so effectively this was called whisper copy. And the idea was to put the fear of stink in women so that they worried that they were going to be socially isolated and excluded from finding a husband. This was like the early 20th century and it worked. It was super offensive, but people were worried about being talked about behind their backs and worried about not finding love. And once they saturated the market for women, they thought, oh, there's like half of the population we've ignored. What are they worried about? And around this time, it was like the late thirties, early forties, which was when there was obviously the Great Depression and a lot of people out of work. And so the strategy that they used on men was less a, you're not going to find yourself a woman, but you're not going to find yourself a job.

Sarah Everts [00:37:05]:
You're going to go into the boardroom and you're going to be stinking like a goat and you're going to lose your job. And so they, yeah, this is why most people in North America use like, deodorants and antiperspirants, because of this, like the success of this strategy called whisper copy. And it's just, it's the fear of exclusion. We're such social animals. That being said, different places have different concerns about this. So, you know, I spent twelve years living in Germany and, you know, not everybody. Where is deodorants? On the subway there. You travel to France and people pair their deodorant perfume with their body odor with this idea that there's going to be an armpit malfunction.

Sarah Everts [00:37:59]:
So you might as well try and come up with something that smells good together and contrast that with North America, where any sign that you smell like a human is met with horror and disgust. And what's so funny to me, and sure, I wear deodorant too, right? Like, I'm a social creature. But what cracks me up is that, you know, you put on deodorants and they smell like, you know, citrus or they smell like spice and it's like, you're not fooling anybody. You do not smell like a citrus fruit, you do not smell like old spice. This is like, not you, you're like an imposter. Um, and yet we all kind of pretend to be these, these have, have these other odors, even though, quite frankly, we all smell pretty similar. Like humans have two chemicals that are top notes in our body odors. So, for example, if you go into an elevator, I don't know if you've ever had this experience and you smell a stinky smell, you can tell if it was a stinky dog that was in there, like a wet dog or a human or a stinky something else.

Sarah Everts [00:39:17]:
But you can tell that there was a human. Even though we kind of all have our own symphony of smell, there's always these two top notes. And one is, yeah, hexanoic acid. It's a derivative of that. And another one is something called, I think I have it written down, sulfonyl hexanol. And one is like, smells like tropical fruit, meats, like onion, and the other one smells like a rancid goat. And those are the two things that, like all humans make that allows you to like distinguish human from horse or human from dog.

Dan Riley [00:39:53]:
Fascinating. I know I mentioned this to you before we started recording, but I have wanted to do an episode on sweating for a long time. And one of the ironies of my life, one of the best things that I do for myself, which I told you, told you before we started recording as well, is I intentionally put myself in high heat, either sauna or heated yoga classes basically every day of my life. And there it is. Less embarrassing to be dumping sweat. Its still not a great look, but typically those classes are a little bit darker and other men, if theyre in there, are typically sweating at least somewhat in the same range as I am. The benefits just psychologically from that sort of heat exposure. I think outside of sleeping eight or 9 hours a night is the best thing I do for my health and its not even close.

Dan Riley [00:40:44]:
Id love to give you an opportunity too to speak to what we know about why sweating. And obviously people do this in other contexts, running or working out. But for me it seems to really get. I get a ton of benefit from 100 degree rooms and 40% humidity for an hour, pushing myself pretty hard. And the endorphin rush or just the improvement in mood and cognitive abilities, um, pro sociality afterwards is. It's like two different humans. It's like I have run the experiment on a day without it and a day with it, and it's like I'm two different people. Um, I'd love to give you an opportunity to speak to the health benefits, um, of a really great sweat, in however much detail you might like to provide.

Sarah Everts [00:41:35]:
Yeah, sure. Um, that euphoria is real.

Dan Riley [00:41:40]:
Yeah.

Sarah Everts [00:41:41]:
So, yeah, I will start off by saying that a lot of spa and yoga places make all sorts of claims about the health benefits of sweating in large quantities. And there are, as you point out, many. But there's a lot of b's too, right? Like, sweating in large quantities is not going to cure cancer. It's not going to cure the common cold. None of these studies have ever been more than, like, one tiny study that had, like, dodgy results. What we do know, though, is that sweating regularly, even just in a sauna or like, in a yoga space, is really, really good for heart health. And I'll explain why. So this is actually a really long range study that was done in Finland, where they have more saunas than cars and almost like, like one sauna per person anyway.

Sarah Everts [00:42:40]:
They looked at like thousands and thousands of people over a very long time and found that people who went to the sauna more often had lower incidences of cardiovascular disease and other health disease, lower incidence of heart attacks. So effectively, going and regularly sweating in a sauna is actually really good for your health. And the way that it was explained to me by the scientists who did that work is that effectively, when you go into a sauna, even though you're not exercising, you are getting some of the benefits of exercise. So if you think about what I was talking about before, where if you start to run, your body starts the cool down process, what is happening when you go into a sauna is exactly the same thing. Even though you are not burning calories, when you're just sitting in a sauna, you are exercising your heart because it's got to move all the blood from your hot interior around to the surface of your skin to cool away, to cool your body down. And so it's really pumping fast, right? Like, you go into a sauna and your heart starts beating fast, even though you're just sitting there. And so it's a great workout for your heart, and you get the benefits, both hormonal. So you mentioned, like, endorphins, right? Endorphins and epinephrine and other happy hormones are produced when your heart gets a workout, right? That's what runners experience and other, you know, spin, people who do spin.

Sarah Everts [00:44:20]:
But that workout, even just sitting in a sauna for your heart, is doing the same thing. And so you get the happy hormones, and then you also get a workout for your heart, which is good for you, just writ large and good for your cardiovascular life. And so that is the science that's very solid on why it is good just to sit in a sauna or to sit in a really hot, hot place and to do some exercise. Of course, I think in your case, if you're doing a little bit of yoga, you're also, like, beautifully stretching, you're probably doing a little bit of exercise and getting some other knock on effects. But just sitting in a sauna, even though it's not burning as many calories as maybe doing jump squats or going for a run, you're still exercising your heart. But I would like to say that, like, one of the biggest myths that these places say is the detox myth that, like, sweating in large quantities is going to help rid your body of nasty chemicals. And this is complete hogwash if you understand how the human body works. So if you remember, when you get the cool down directive and start to sweat, your sweat glands are sourcing that liquid from your blood, right? So that means anything that's circulating around in your blood does come out in your sweat.

Sarah Everts [00:45:42]:
So that means good stuff comes out, like vitamins or hormones or a little bit of that alcohol that you took too much of the night before. Also things like lactic acid, also bad things like urea or if you have heavy metals in your blood. Anything that's circulating in your blood that is smaller than a red blood cell, that's just like a molecule that's going to come out. But that's not how you rid your body of that bad stuff. Because if you think about it, to get all that, that bad stuff out, you would literally have to sweat out all the liquid in your blood that would leave you completely dehydrated and most likely dead instead. Right? You have kidneys that filter your blood for that crap and send out that crap and pee. Anything that comes out in your sweat, it is a sign of what's happening in your blood, right? It's a sign of what's happening inside, but it's not how you are getting that stuff out. It's not how you're like, like, getting rid of it or purging your body.

Sarah Everts [00:46:48]:
It's just coming out, incidentally. But it's also kind of interesting from a surveillance side because, of course, you know, when you drip, you know, a little bit of sweat on your yoga mat, you're not just revealing that you're a sweaty dude and doing some exercise, but if you were doing drugs or if you know all sorts of other information, if it's circulating around in your blood, that's going to come out in your sweat as well. So scientists are actually and particularly forensic scientists are looking at ways to learn about people at crime scenes from the sweat they leave behind, which is typically in fingerprints, because, like, a fingerprint is just a sweat print. And up until now, most forensic scientists have looked at those prints and how they look and compared them to databases of known criminals. But if there's. If you're not a known criminal but you commit a crime, you're not in that database. But now they can lift a fingerprint, and instead of just looking at how the whorls and swirls appear kind of artistically, they can actually measure the chemistry of the leftover sweat you left behind and find out if you are high on cocaine, if you're a meat eater or vegan or anything like that. I had my fingerprints tested, and they could tell that I had a coffee because there was caffeine left over in my fingerprint, and had I spiked my coffee with a little bit of whiskey, Bailey, as I'm known to do.

Sarah Everts [00:48:26]:
Yeah, that would have come out, too. And already, law enforcement is doing kind of proof of principle tests. Like, they lifted a fingerprint from a windowsill where a stalker tried to break into a woman's house and found out that the guy just from fingerprint had been drinking and high on cocaine. So, you know, this is both really interesting. Um, it's interesting for athletes because you can learn, um, from your sweat if you are exercising aerobically or anaerobically because different levels of lactic acid are produced. So if you're, like, training for a marathon versus a sprint. Right. You might want to adjust your.

Sarah Everts [00:49:07]:
Your exercise using, like, a device attached to your finger. On the other hand, um, you can also learn if, you know, you have cancer or you can learn if you're doing drugs. And what if in your workplace, somebody lifts this from your cubicle and finds out that you come to work high? So there's, like, all sorts of interesting privacy and surveillance things that are coming out from just the fact that sweat is sourced from the liquidy parts of your blood.

Dan Riley [00:49:40]:
Fascinating. And so it's. That's obviously not a blood draw, but some of the data that one can get from a blood draw seemingly can also be obtained through sweat analysis.

Sarah Everts [00:49:51]:
Yeah. So that's what people are hoping for, because, of course, a blood draw is, like, traumatic for some, and it also, like, requires a needle. And so people are really interested to find out different sorts of things. Like, can you diagnose some diseases this way? Can you? Yeah. Like, could you? I mean, the holy grail is blood glucose levels, because, like, folks who have diabetes, have to have a small needle in their arm completely, always measuring their glucose level. This is really tricky because we have bacteria on our skin, and so as soon as the glucose comes out, the bacteria eat it. And so it's very hard to, like, really measure glucose accurately. But in terms of things like, the next time in ten years, you go to a pub and your smartwatch is in contact with your skin, and after five beers, you get a push alert saying, dude, take a cab home, or an uber or whatever we're using then.

Sarah Everts [00:50:56]:
Or you have a car that has a fingerprint starter, and the insurance company requires that that fingerprint shows no signs of alcohol for you to be able to start the car. Or you can imagine long distance truck drivers or pilots get tested just before they get into the cockpit to test them for their state of affairs, or last but not least, sports teams. So you can imagine if you have, like, a soccer match or a football match or whatever, a basketball, and somebody has, like, a sweat patch that's measuring what's coming out in their sweat. Well. Well, when you start making stress hormones, that usually indicates that your performance is probably going to start to plummet because you're at your max. So if you're a coach on the sidelines with an iPad and you are monitoring the biochemical signals in the sweat of all your players, you can be like, yeah, let's pull that person out and put this new, fresh player in.

Dan Riley [00:52:02]:
Fascinating. I know we're getting close to the end of the conversation, and I want to close by, um, doubling down on some of the potential health benefits of sweating. And, you know, you were just talking about stress hormones and cortisol. And it has always been my intuition that part of what I'm doing when I'm doing these daily exercises is releasing cortisol, or that there's something happening where my stress levels are getting massively reduced. I've often said to friends that, um, that daily practice, for me, brings any day, on a scale of one to ten, up two or three notches is. And part of that is just a reduction, a massive reduction in stress and just general anxiety. I know there's data that I've read about related to how sauna practitioners seem to have a massive reduction in all cause mortality, something like 40%. For people that are doing sauna practices four or five times week.

Dan Riley [00:53:07]:
It's a long way of me asking, is it really? It's not necessarily, if I'm understanding you correctly, the sweat that is leading to those sorts of benefits, it's more the heart stress, stressing the heart, that's leading to largely the positive effects on your psychology and the positive effects on your general biology. I've had an intuition, too, that I'm basically intentionally inducing a mild fever every day. But I would love to put it to you and get your thoughts on any of that or all of that that you might like to respond to.

Sarah Everts [00:53:49]:
Yeah, well, I mean, I think there's so much to be said for forcing your heart to exercise, and all sorts of, like, other things benefit from that. So, and this is work that's been done in animal models where they put, like, little hamsters into saunas and they look at the chemicals that are produced in their blood when they're forced to heat up. And that exercising of your heart, right, it's not just giving you the happy hormones. Like, do not underestimate the power of a happy hormone, right? Like, we produce things that give us euphoria. Think of, like, the joy that you see when you see somebody that you love or a beautiful landscape. Like, you literally feel a joy, and that is chemistry. That's like your body producing happy hormones. And so don't underestimate the power of the production of those happy hormones.

Sarah Everts [00:54:45]:
And your body wants you to continue doing things that are good for your body, right? So, like, exercising your heart is good for your body. It leads to a longer life. And so your body wants to give you a little perk on the side. It's like, good boy here, right? So, like, you are getting benefits because your body knows that this is good for your heart. And also there's the production of enzymes that, like, for example, break down plaque in your circulatory system that's got overall benefits for reducing the chances of things like stroke and other. You've got to imagine that benefit working out. Your heart has tons and tons of downstream effects, and your body wants you to keep doing that so that you can live a long, long, healthy life. So I think that that's what it's about.

Sarah Everts [00:55:42]:
And I think we are really good at thermal regulation. Like, that is our amazing skill set. It has benefited humans for as long as we've been hairless apes. Right? It behooves us to lean into that.

Dan Riley [00:56:01]:
Love it. I love your work. I love this subject. I really appreciate you taking time to talk to me and my audience about the subject. It was really wonderful to talk to you.

Sarah Everts [00:56:12]:
It was really a pleasure.