Long before advertisers convinced us that sweat was a defect to be battled, the ancient world prized perspiration, according to Bill Hayes, author of “Sweat: A History of Exercise,” out Jan. 18.

Hayes, an avid exerciser and partner of the late writer/neurologist Oliver Sacks, writes that the sweat of athletes in the ancient world was a hot commodity. Athletes would scrape their secretions and sell them — charging the equivalent of thousands of dollars today for a few drops.

“This presumably funky-smelling mixture, called gloios, was considered so precious that some went so far as to take scrapings from bathhouse walls against which athletes had leaned and left sweat tracings from their bodies,” Hayes writes. These secretions were used not to help with athletic performance, but oddly, to “treat the most uncomfortable maladies on one’s most private parts — hemorrhoids and genital warts.”

The ancients were way off the mark — no doctor would dare suggest putting stranger’s secretions on STDs — but sweat is actually quite an impressive substance. While the majority of Americans still spend billions to mask or minimize perspiration, Sarah Everts, author of “The Joy of Sweat: The Strange Science of Perspiration,” calls it our “biological superpower.”

Sweat not only keeps us cool, but also holds key information about our lives, and may even communicate genetic compatibility with possible mates. A famous study from the 1990s suggested that women can sniff out the compatibility of men’s immune systems with their own by smelling their sweaty T-shirts. The sexier the odor, the better an immuno-match.

We are born with all the sweat glands we’ll ever have (anywhere from 2 million to 5 million) and a mixture of genetics and environment affect how they work. Some of us are just plagued with sweatier genes and are naturally more inclined to drench our shirts. At the same time, those born in a hotter climate also have more active glands for life.

Sweat is made from the watery base of our blood minus the red blood and immune cells. “Nicotine, cocaine, garlic odor, food dyes, amphetamines, antibiotics — they all trickle out this route, whether we like it or not,” Everts writes. 

Our underarms produce a different kind of sweat than the rest of our bodies, secreting thicker stuff made of proteins and fatty acids akin to earwax. But armpit sweat itself is odorless. Rather, thebacteria it attracts is what creates the stink, which has often been described as “wet dog,” “rancid butter,” and “cooked onions.” (According to the Journal of Investigative Dermatology, 2% of people have a gene that makes their armpits odorless, though 75% of these lucky few still wear deodorant.)

When we don’t sweat properly it may be a sign of medical concerns, including diabetes, alcoholism and Parkinson’s disease. Blunt trauma to the skin can also curb our ability to sweat, making us more susceptible to deadly heat stroke. 

Sweat could eventually lead us to intriguing scientific breakthroughs. Researchers are currently working out how to harvest the energy from sweat to power biomedical devices — essentially turning the self-made liquid into biofuel. And, one day, doctors and even detectives might be able to use sweat to reveal our deepest, darkest secrets.

In an interview with NPR, Evert explained that a kind of sweat “fingerprint” could tell if a person was “drinking alcohol or that person actually has cancer. All sorts of private information is being left behind in the drips we leave on our yoga mats but also literally on everything that we touch.”

Meanwhile, it seems that younger generations — just like the ancients — are happy to embrace their sweat. Gen Z claims to wear much less deodorant than the rest of; nearly 50% hadn’t bought any in a year, according to a 2019 poll.

In being comfortable with their own body fluids, the young are onto something, Everts claims.

“Sweat has received enough side-eye,” she says. “It’s time we all found some joy in sweat.”