Sweat is an evolutionary miracle that allows people to outlive and thrive: gunshots
Cavan Images / Getty Images / Cavan Images RF
Cavan Images / Getty Images / Cavan Images RF
You think sweat is disgusting?
“It could have been SO much worse,” says Sarah Everts, author of a new book called The Joy of Sweat, which is about the science of sweating.
It turns out that human sweat – our body’s air conditioning system – is actually quite tame on the “Him” scale of animal cooling methods.
Dogs drool to keep cool while vultures poop on their legs and seals urinate on their feet, she says. If you think about what evolution might have left us, says Everts, “sweat is a million times better.”
In fact, Everts said NPR’s Short Wave, instead of viewing sweat as gross, consider it an “evolutionary wonder.” She even calls it a super human power and a highly efficient one at that. “We effectively divert water to our skin, and as it evaporates, it draws heat away from our bodies,” she says.
Everts points out in her book that it is this superpower that enables people to thrive and dominate all over the world. “Sweating allowed us to look in the sun without overheating, while our predators were relegated to the shadows to survive,” she writes, adapting to many new environments. “Like the (city) pigeon and the desert pigeon, we can survive almost anywhere.”
Short Wave’s Rhitu Chatterjee spoke to Everts about the incredible science of sweat, which has made it possible to include facts that most people don’t know. Get this: How much you sweat is influenced by both nature and care. And did you know that you can sweat in different colors? Yes, both are true.
Check out the fascinating interview from Everts below. Don’t have time to read it? No sweat! You can listen to it by clicking the audio link above.
This interview has been edited for clarity and length.
In your book you write that sweating is human. How much someone sweats is a mixture of their genetics and where they grew up, right?
It’s kind of interesting because these glands – they’re called eccrine glands – you are born with all the eccrine glands you will ever have. But these glands only become fully active in infancy. And so, at these very early years of your life, your body learns about the climate you are in. And researchers are trying to find out how much the environment you spent your early years in ultimately affects how much you sweat as an adult.
That is the maintenance part. But there is also a natural part. Some people and some families are just more sweaty than others. And maybe you have more sweat glands than average. Most people have between two and five million.
I got mine counted. I have three million! And there is also the flow rate, correct. So some people are very efficient with their sweating and some just open the floodgates. And that may have to do with genetics as well, but it may also have to do with acclimatization and your body learning on the go.
I mean, athletes do it right. When preparing for the Olympics in a really hot place, they will try to exercise in very similar conditions so that their bodies learn to cool down efficiently in such an environment.
You write in the book that sweat contains so much more than water.
Oh yeah! So that was what really blew me away. When you think of sweat, it took me a long time to write this book to ask: where does it really come from? It is effectively the liquid parts of the blood, minus the big things like red blood cells and platelets and immune cells.
So when you open a body, you are very wet inside. Right. You have this thing called interstitial fluid that keeps all of your organs moist and moist. And this fluid is made from blood. And when your body receives the cooling order, your sweat glands draw sweat from this interstitial fluid. So literally anything in your blood can leak through.
So the evidence of my morning coffee comes out in my sweat. When I have a gin and tonic on a hot day, the alcohol definitely comes out. Evidence of the food we eat, evidence of our health, or even how we move about.
There is a story you write about in the book: The South African nurse whose sweat turned red.
Oh to be that woman. She was a nurse and wore a white uniform and noticed that her sweat was red. And that’s a very strange situation, isn’t it?
She was very unsure about this and went to a dermatologist. But they couldn’t find out what was going on for a long time because she was in her mid-twenties, she was perfectly healthy. They checked her for everything.
One day she comes to the clinic for a follow-up appointment and one of the doctors notices that her fingers are reddish-brown in color. It turned out she had a snack before the appointment and it was this corn chip called Spicy Tomato. She liked these chips very much. She ate several bags a day – so much. The dermatologist called it a fetish.
They analyzed their sweat for the same dyes and dyes as the chips and found a match. And so effectively did her red sweat disappear as soon as she reduced her fondness for those special chips. But other people have turned into all sorts of colors for all sorts of reasons. It’s a fun little corner of the medical literature called Chromium Hydrosis: Chromium, Bright, and Hydrosis for Sweat.
What about the other components that come out in sweat? Do you have a role? And what makes sweat stink?
What’s coming out of your sweat pores – the whole medical job is to keep you cool. But in doing so, your body also sends out some proteins that take control of your skin’s microbiome. Right. So help the helpful bacteria thrive and try to keep pathogens at bay. But most of what comes out of that watery sweat called eccrine sweat is exactly what happens to be flowing around your body.
Of course there is another kind of sweat: the stuff that makes you really stinky. It’s the sweat that comes out under your armpits. It’s actually a completely different type of sweat gland. It’s called the apocrine gland and it becomes active during puberty – as many of us know.
And that’s not salt water at all. It’s a bit like waxy, a bit like ear wax, but much longer and the bacteria that live in your armpits eat and metabolize that sweat, effectively pooping out the body odor that comes out of your armpit.
So the body odor changes depending on the sweat content and the mix of bacteria that metabolize sweat?
Exactly. And so we all have a unique body odor print, right? We all have our own smell. And that’s effectively the mix of waxy molecules that come from those apocrine glands plus the unique ecosystem of bacteria that live in your armpit. And this combination gives you your unique smell print and mine. And it enables dogs, for example, to track people if they have sniffed out something they were wearing.
You write that sweat is barely understood by scientists. What do we not yet know about sweating and what are the researchers investigating?
Some of the really interesting areas are the development of the sweat glands and how we actually created one of the most efficient ways to cool off 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 ongoing. [Researchers are] try to do the forensics of science, for example – like monitoring what comes out when we sweat and monitoring what the chemical residue in a fingerprint is. Because a fingerprint is just a sweat print. And forensic scientists can now learn everything about your biological identity from the chemicals actually left in your fingerprint.
If you can analyze the chemicals on that fingerprint and figure out wow this person has, you know, drank alcohol or that person actually has cancer – all sorts of very private information is left in the drops we leave on our yoga mats, but also literally on everything we touch.