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Eight healthy men in shorts and t-shirts. Average age, 26.  

They’re covered in sensors, wires dangling, like marionettes at rest. As they sit together in silence—blindfolded—they wait for their 10 minutes of psychological torture to begin.

These guys are part of an experiment in perspiration. Most human sweat is the “thermal” kind, that dampness you feel during a workout or on a hot day. But psychological sweating is the beading on your forehead when your boss singles you out in a meeting, or the clammy hands you wipe on your jeans before a first date.

That’s why these human lab rats are here.

So what kind of torture would evoke nervous sweating in the laboratory? Being asked to deliver a speech in front of a crowd? Having to strip naked before a panel of hot female scientists? Nope.

“Subtraction, addition, multiplication, division,” says study author Nigel Taylor, Ph.D., of the University of Wollongong, Australia, who’s investigated human sweating for more than 20 years.

The men had to do math—just basic problems, says Taylor.

“They were certainly within everybody’s capacity.” Faced with problems like “1,654 + 73,” every man started dripping with sweat.

We have a complicated relationship with perspiration. At the gym or on the court, it’s welcome in abundance—not just for its physiological cooling function, but for what it says about our exertion levels and competitiveness.

Anarchy Workout

But psychological sweating—nervous perspiration—is something else entirely. It’s a physical response we try to avoid or, failing that, hide.

In a Men’s Health survey of nearly 800 guys, 73 percent said they wish they’d sweat less.

Our romantic interests wish we would too: Of 970 women surveyed, 84 percent deemed it gross when a man dews up on a date.

“Involuntary sweating is like your body betraying you,” says Carisa Perry-Parrish, Ph.D., a psychologist at the Johns Hopkins Center for Sweat Disorders in Baltimore.

We want to appear confident, but our bodies scream, “I’m freaking out!” Then we go from sweating because we’re stressed to stressing because we’re sweating, says Perry-Parrish.

Next thing you know, you’re in the men’s room aiming the hand dryer at your pits.

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The first step toward sweating less lies in understanding the source.

You have two types of sweat glands, apocrine and eccrine. The apocrines are located mostly around your armpits and genitals and produce a thicker, stickier sweat consisting of proteins and lipids.

The eccrines cover your entire body and produce a solution that’s mostly water and salt.

Scientists used to think the eccrine glands were activated only by a need to cool, and the apocrines by mental stress. But Taylor and his colleagues recently confirmed, in a series of precisely controlled experiments, that both types of sweat can be produced by the eccrine glands and controlled by a single neurotransmitter called acetylcholine.

That means whether you’re running 5 miles or trying to seal a deal for $5 million, both sets of glands are working. Though clammy hands are the most obvious sign, psychological sweat can be a whole-body experience.

This finding lends support to one evolutionary explanation for why stress makes people perspire: If our skin became slippery in a fight-or-flight situation, predators wouldn’t have been able to grab and hold on to us.

Another theory, notes Daniel Lieberman, Ph.D., an evolutionary biologist at Harvard, is that sweat could help aid a quick escape from danger. Most mammals, including those from which we evolved, have sweat glands on their paws.

“Imagine that you are a small furry animal in Africa and you catch sight of a raptor swooping down to kill you,” says Lieberman. “Moistened paws will help you scamper up a tree or cliff by creating tiny little vacuums.”

It works the same way that a licked finger helps you turn a page in a book.

The Better Man Project

Nervous sweating may also have helped us save our clan. In a U.S. military study, researchers collected sweat from people during two tasks: running on a treadmill, and skydiving for the first time.

A separate group of volunteers were then hooked up to brain scanners and asked to smell the collected sweat. Nothing interesting happened when they sniffed the treadmill drippings. But the scent of skydiving sweat triggered the parts of their brains associated with alertness—they could literally smell fear.

In other words, perspiration could have warned others that there was a whiff of trouble in the air.

In fact, your body odor can act as a health indicator to you and others close to you, says Pamela Dalton, Ph.D., M.P.H., a researcher at the Monell Chemical Senses Center in Philadelphia.

Sweat itself is actually scentless, but as it interacts with the bacteria living on your skin, the combination gives off a musty smell—a.k.a. your BO.

But your scent can change when you’re fighting off an illness: A study published in the journal Psychological Science found that people can detect a difference in body odor when someone becomes sick. The researchers think an ill person emits a different chemical cue that signals the activation of the immune system.

This specific scent may warn others to keep their distance.