The science of sweat: What happens when you’re feeling hot

In The Joy of Sweat, Sarah Everts explains the ‘vital life process’ and dispels its myths

The Joy of Sweat
The Joy of Sweat
Author: Sarah Everts
ISBN-13: 978-0393635676
Publisher: WW Norton & Company
Guideline Price: $23.95

In The Joy of Sweat, an entertaining and illuminating guide to the necessity and virtues of perspiration, science journalist Sarah Everts points out that plenty of people pay good money to exude sweat while also paying good money to hide it. Saunas, spin classes and hot yoga, yes; but also deodorant, dress shields and antiperspirants that deliberately create what Everts calls (vividly and unappetisingly) a "sweat-pore plug".

“This vital life process, one that we all possess, one that helps make us human, is deemed embarrassing and unprofessional,” Everts writes. “How did that come to be?” Sweat helps to keep us alive. The human body produces a lot of heat, even when it seems to be doing nothing. Start to move and exert yourself, especially when the weather itself is hot, and your body will produce even more. Our eccrine glands, which Everts describes as “tiny, elongated tubas embedded in skin” with “extensive coiled piping” at the base, release fluid that evaporates off our hot skin. Without this mechanism, our bodies would succumb to heatstroke, with organs failing, blood haemorrhaging, bacteria breaching intestinal walls.

Then there’s the other kind of sweat, which comes from the larger apocrine glands, located in places such as the armpits and the groin. These glands ooze “waxy, fatty molecules” that are especially appealing to bacteria, whose feasting produces a chemical waste. This waste is what stinks. Sensory analysts have identified the component scents in human armpit odour, which include “rancid butter” and “wet dog”.

We could urinate on ourselves if we were seals, vomit on ourselves if we were bees, or defecate on our own legs if we were storks. Instead, we release sweat

But the human cooling mechanism could be much worse, Everts says – less effective and even smellier. Nonhuman animals either don’t sweat, or they don’t sweat as efficiently as we do. (To “sweat like a pig” would entail not sweating enough, so that we would have to roll around in the mud to halt overheating.) Some scientists posit that our cooling system is what allowed humans to forage for food in the sunshine for hours while predators languished in the shade. Everts tries to shock us into appreciation by pointing to alternative methods for cooling down. We could urinate on ourselves (like seals) or vomit on ourselves (like bees) or defecate on our own legs (like storks). Instead, we release sweat – a passive act that has the added benefit of not creating its own heat.


Everts is a crisp and lively writer; she has a master's degree in chemistry, along with an ability to put abstruse scientific processes into accessible terms. She tethers her scientific interludes to scenes in which she's doing some unlikely things around the world – getting her armpits sniffed by an analyst in New Jersey, participating in a "smell-dating" event in Moscow, watching a man engulfed in a dry ice vapour during a "sauna theatre" performance in the Netherlands.

She dispels some persistent perspiration myths, including the one that equates sweating with detoxification. The book opens with the story of a South African nurse whose sweat had turned red because she liked NikNaks Spicy Tomato corn chips so much that she was consuming six bags of the red snacks a day. But the anecdote turns out to be a bit of a red herring (sorry); Everts is just warming up (sorry again). Traces of red just happened to come out with the nurse’s sweat because “the human body is inherently leaky”, Everts writes, “not because sweat is the way your body intentionally expunges toxins”.

Everts is a crisp and lively writer; she has a master's degree in chemistry, along with an ability to put abstruse scientific processes into accessible terms

A lot of our hang-ups about sweat turn on the issue of smell. This is especially true in the United States, where the analyst who sniffs Everts' armpits observes that – unlike in the expert's native France – scent consumers are looking not to complement their body odour but to ensure its "annihilation". Our attitude to smell isn't exactly one-note, though. Everts also examines the cultural obsession with pheromones, and the idea that odour messages are somehow irreducibly authentic.

We can try to cover them up, but we can’t calibrate them – hence the smell-dating event or the peddling of pheromone colognes that are supposed to make men irresistible to women, though their efficacy is dubious. “The problem is these products are more likely to attract a horny sow rather than a horny human female,” Everts writes.

For obvious reasons, this is a summertime book, and Everts keeps it light, even if her subject has some unavoidably serious implications. She makes only passing mention of Covid-19, in a passage about the various ways that human greetings have allowed for a moment of increased proximity “wherein we can, at least theoretically, take in the odour of another person”. Another passage about anosmia – the inability to smell – doesn’t mention the pandemic, even if loss of smell has been one of the coronavirus’s symptoms.

The biggest crisis looming over the subject, which Everts explicitly acknowledges at several points, is global warming. “Our ability to sweat may be foundational to the resilience we’ll need to get through the coming climate apocalypse,” she writes, though the excess humidity that comes with changing weather patterns may render our sophisticated cooling mechanism moot. When it’s too humid, sweat can’t evaporate.

Not to mention that global warming could melt some old plagues out of the permafrost, including some mysterious sweating diseases, such as the Sweate in medieval England, which killed people within five to six hours, or the Picardy Sweat, which may have killed Mozart.

Understandably, Everts nudges the reader away from staring too long into the existential abyss. She’s as fascinated by the ambiguities of her subject as she is by the certainties she can pin down. One thing I couldn’t stop thinking about was how each person’s individual scent combines with another person’s individual scent receptors. “Even if you think you know your own smell,” she writes, “you may not know how others are experiencing it” – a terror or a comfort, depending on how you see (or smell) it. – New York Times