Cameron Muir thinks a lot about hot, sweaty sex.

It’s his job, after all. Muir is a psychologist at Brock University, and his current fascination is human sweat — particularly when it’s coitus-induced.

His interest in sweat was aroused by steroid hormones, the tiny molecules like testosterone and estrogen that control so much of human sexuality from the inside of our bodies. Testosterone, in particular, can profoundly change a person’s appetite for sex.

Women who have had their ovaries removed often complain they’ve lost their libidos, probably because of changes in hormone concentrations. “They’ll go to the doctor and say I’m married, I have no sex drive, and my husband doesn’t like it,” said Muir. “What the doctor will do is prescribe testosterone.”

The testosterone usually comes in a cream that women rub on their bellies—steroid hormones are small enough to be absorbed through the skin.

The treatment started Muir thinking. What if he could find a natural version of testosterone cream in men’s armpit sweat? Sure enough, he discovered that when men vigorously exercise, they did indeed sweat out small amounts of testosterone.

Furthermore, when that exercise is sex, they excrete much higher amounts of the hormone. “The concentration is more than ten times higher, and that concentration is almost as high as the concentration doctors would prescribe for women to enhance the libido,” said Muir.

All of which suggests to Muir that testosterone may act as a pheromone in humans. “During sweaty sex, a man might transfer his testosterone to the female, turning her on even more,” he said.

More importantly, his findings and theories are helping revive the decades-long debate about whether human pheromones even exist.

Pheromones act as silent messengers between animals—they are molecules that are secreted by one animal and perceived by chemical receptors in another.

“When you see a dog sniffing a fire hydrant, he’s not smelling it per say, but he’s getting information about who was there recently, and what kind of state they’re in,” said Muir. “Is there a dog in heat around here? Is there a dog defending its territory?”

Whether pheromones are at work in humans is another matter. Martha McClintock, now of the University of Chicago, did the first study on human pheromones when she was an undergraduate science student in 1971. She observed how the menstrual periods of the women in her dorm slowly became synchronized, and suggested that a pheromone in their armpit sweat was responsible.

Her research remains contentious. Scientists agree that her methods were sloppy, and some detractors still use her study’s shortcomings as an argument against human pheromones.

Unreliable methods continue to haunt pheromone researchers, and the financial interests of some of their colleagues aren’t doing anything to raise the reputation of the field.

The Athena Institute in Pennsylvania is a leading producer of human pheromone research. They claim to have discovered pheromones that make men and women go wild for each other and they’ve published their results. But the results can’t be replicated in other labs because the formulas of the pheromones are secret—and the Institute sells them in vials on the Internet.

Muir says the biggest debate in the human pheromone controversy is about where humans receive pheromonal messages. For most animals, pheromone receptors are in something called the vomeronasal organ—the organ at the back of a snake’s mouth that she touches her tongue to in order to “smell” her surroundings

“The vomeronasal organ is well understood to be involved in transmission of chemicals from one animal to another,” said Muir. “Humans do have a vomeronasal organ, but it doesn’t seem to be functional. “

But there is mounting evidence that mammals send and receive chemical cues. An American study in the journal Nature last month identified a new mouse pheromone. The researchers also zeroed in on the receptors that accept the pheromone’s message—they’re in the olfactory bulb, the organ responsible for smelling, and not the vomeronasal organ. A similar system is possible in humans.

Muir’s research indicates a third receptor for pheromones, beyond the vomeronasal organ and the sense of smell. Steroid receptors beneath the skin might be all that’s needed for human pheromone transmission.

“We don’t need a vomeronasal organ. If you can drip sweat bursting with testosterone onto a female’s belly during sex, this might explain what’s going on,” said Muir.

He now wants to look at a distinctly human behaviour—kissing, which is often a precursor to sex. The human mouth is full of testosterone receptors, and Muir wonders if there’s a high concentration of testosterone in saliva. “Why would you have steroid receptors in your mouth if it weren’t for a reason like this?”

Muir is also concerned that his studies reflect a common bias in sex attraction research that says males are the only sex competing for mates—most human pheromone research focuses on how men can attract women, not the other way around. Muir hopes to help correct this, and begin research that would look at how women use chemicals to turn men on.

There is already some research into how men react to steroid hormones, which can also be inhaled in high concentrations. A European team has found that men who are sprayed with estrogen will confuse male and female faces—effeminate men start to look like women. Another group has shown that homosexual men (and heterosexual women) prefer chairs that have been sprayed with testosterone.

Muir expects that the skepticism over human pheromones will keep the pace of research moving at slug speed. To support his pheromone studies, he has been forced to divert money from other projects.

“I just can’t seem to get funding for this research,” said Muir, “I’ll hand in my grant application, and one referee will say ‘you’re right, this is great’ and the other referee will say, ‘I’m sorry no, I don’t believe in human pheromones,’ and you have to have both of them to get the grant.”

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