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Working out and working up a sweat go hand-in-hand. But perspiration is about much more than keeping cool. According to Dr Vybarr Cregan-Reid it also sets humans apart from other animals, and has helped us climb to the top of the evolutionary ladder.

MARGO WHITE: Why do we sweat?

DR VYBARR CREGAN-REID: We have different kinds of sweat that is produced on different parts of our bodies. It’s mainly our thermoregulation technology, which allows us to stay cool on a hot day. It also creates our scent, our body odor. Everybody knows about the smelly parts, the groin and armpits, but that involves different types of sweat glands, to create a specific scent that is as unique as our DNA. But the main function of most of our sweat glands is thermoregulation.

Before we go on, you’re a lecturer in Victorian literature, so how did you become so interested in (and a bit of an expert) in sweat?

It’s all because I wrote a book on running, Footnotes; How Running Makes us Human. A lot of that is about how running inculcates creativity, how this almost meditative activity has very specific neurological effects on the brain. So I’d go out for a run, and come back with an idea, and this interest in sweat was one of them. It suddenly became clear, when I was out running, that sweat is an evolutionary imperative that has given us an advantage over other mammals, in terms of hunting.

Sweat is about as essential to being human as having a brain is, and has played a key role in the evolutionary success of our species. We think of it as a sort of throwback to our previous animal selves, but the reason we’re at the top of food chain is partly due to the fact we sweat, but also the way we sweat, on particular parts of our body.

Can you elaborate?

We are terrible sprinters, as a species. Animals the size of our palm can run faster than we can. But in certain environments, we have distinct advantages over other animals, because animals, like antelope or deer, aren’t able to lose heat as efficiently as we can. And because they’re quadruped, more of their body is exposed to sun on a hot day. So not only do they capture more heat from the sun, but they’re less efficient at losing it. We’re two-legged so we’re slower, but we don’t take on as much heat, and we have efficient cooling technology all over our body.

So two legs are better than four?

Yes, if you start chasing an antelope, it will skip away with the airiest disdain. But if you keep plodding along, at a jogging pace, you’ll catch up with the antelope. It will run away again, but once you’ve repeated this several times the antelope won’t be able to lose enough heat and will get to the point of heat exhaustion. Any animal that is good at sprinting is not good at running long distances, but many aspects of the human body are optimized for running long distances.

But horses sweat, don’t they?

Horses are the only animals that sweat in a way that is most similar to the way humans sweat. But they have a sort of waterproof coat, so they have a different protein in their sweat that allows it to foam up, pass through their waterproof coat and evaporate. So horses lose heat by sweating and we do too, and when you compare us to other animals, we really shift a lot of heat.

As you said, there are types of sweat, released on different parts of the body.

We have two main kinds of sweat glands, eccrine and apocrine. Eccrine glands – the thermoregulation glands – are the most numerous type. They’re found all over the body, particularly on the palms, soles of the feet and forehead. Having eccrine sweat glands on an exposed forehead, for instance, means the blood going to your brain is kept cool, so we can think while we’re in motion. The top of the head, meanwhile, is shaded by hair, so it also takes on less heat. I think that’s amazing.

The other type of sweat, the apocrine sweat, is mainly for scent and found in the armpits and the groin. Unfortunately for us, its job is to smell – it’s like our olfactory fingerprint. And because it’s released in areas where it can’t evaporate quickly, it comes into contact with bacteria, starts to break down, and starts to smell. It’s a different kind of sweat, with a different function.

The sweat on our arms, legs and forehead doesn’t smell because there’s quite a lot of salt in it, and the bacteria doesn’t like it. This means it usually gets to evaporate before bacteria get to work on it.

What about the smelly feet?

The sweat from our feet doesn’t smell like the sweat in our groin or armpits. The sweat on our feet is clean sweat, but the problem is that our feet stay covered for such long periods. Shoes have been around for a long time, about 40,000 years, but we’ve been around for two to three million years, on and off. We have smelly feet because we put them in a warm closed-in environment – we put them in ten-inch coffins, which gives the bacteria plenty more time to go to work. If you wore something similar on your hands all day, your hands would smell too.

We tend to have mixed feelings about sweat ...

In certain environments, like the gym, it’s a badge of honor, but taboo in other situations. In job interviews it’s rather awkward when someone goes to shake your hand and you have sweaty palms.

The reason you have sweaty palms is you’re having a fight or flight response. If you have sweaty palms you can run and climb up a tree more easily, because sweaty palms gives you extra grip to hold onto things. But it’s an evolutionary throwback, something that happens when adrenaline is released. So sweaty palms and feet might have made sense, because it would enable you to grip better if you were running or climbing.

Do men sweat more than women?

No. There’s variability across our species, and some people will sweat more than other people, and that’s partly to do with the variability in our DNA. But I can’t believe that women sweat less than men. I think there are more taboos around women sweating than there are around men sweating. Things are beginning to change, but for too long there has been this idea that it isn’t a womanly thing to do, which I think is a tragedy.

Dr Vybarr Cregan-Reid is Reader in English and Environmental Humanities at the University of Kent, and author of Footnotes: How Running Makes us Human. He is currently working on his third book, Primate Change: how the world we’ve made is remaking us.

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