What Do We Actually Know About Pheromones?

The smell of love, what is that? Lemon oil? AXE?
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What makes someone smell good? How do we come to link everyday smells with particular people, and what's that indescribable something extra that makes a blanket smell like more than the sum of its parts? Not just soap and cologne, but him.

"If you, as a human, don't have a sense of smell, it doesn't render you behaviorally incapable."

First discussed in 1959, the word pheromone originally referred to the unique chemical cocktails emitted by animals and detected by members of their own species. Essentially, a pheromone is a chemical combo that, when emitted by an animal and detected by the vomeronasal organ (located between the nose and mouth, which directs stimuli to the hypothalamus instead of the brain's cortex) of another, produces some kind of response -- either behavioral or physiological. We've observed specific pheromone release and response in many animals, but not in humans -- and while we may have vomeronasal organs, most argue that they're vestigial at best.

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Regardless of the lack of evidence for these chemicals in humans, many companies market and sell products meant to boost sexual attractiveness based on the presence of so-called pheromones. James Kohl, a chemical researcher who now sells a line of such products, says that our lack of strict responses to certain chemicals doesn't indicate their nonexistence, but just a high level of self-control. He uses the analogy of food odors: Humans respond to them by salivating, but we can choose not to eat. "The truth," he says, "is that some people control themselves better than others. We're not like other animals, which is why we don't respond to pheromones like other animals!"

But Kohl's products, which he likens to food spices ("They give you an extra kick!"), make some researchers roll their eyes. Dr. Jim Pfaus, professor of psychology at Concordia University in Montreal, is one of them.

"Products containing 'pheromones' are meant to drive women crazy, and they might just work -- on female pigs," he says, referring to the steroid androstenone. Found in the saliva of male pigs, the smell causes females in heat to assume a mating stance. Because humans also produce it, mostly in their urine, researchers have tried to pinpoint it as a human pheromone. Dr. Tamsin Saxton, a psychologist from Northumbria University in Newcastle, UK, recently completed a study that suggested some positive effect on female human attraction to men after the application of androstenone on the upper lip, but stated in the paper that she and her colleagues "wish to distance ourselves from what we see as the naive search for a human sex pheromone that encapsulates much of the media's coverage of the research" and later said that what makes a human smell "good" is "harder to pin down" than many realize.

Pfaus doesn't reject the idea that humans might produce and respond to pheromones, and that these chemicals might be what gives each of our scents that certain je ne sais quoi.

"There are two camps of people," he said. "Some say we must all be sensitive to pheromones, because in the spring time, when the clothes come off and there's more to smell, we all get really happy and into each other. But on the other hand, maybe we're happy because it's warm, and we're more attracted to each other because we're showing more skin."

"The truth is that some people control themselves better than others."

But he doesn't think that's what's important, anyway. Pfaus, who spends his time studying rats and their sexual response to smells, thinks that body odor itself is enough to keep me sniffing my pillow.

"They live in an olfactory world," he said of his rodents, "so odors mean a great deal to them." So much so that they condition themselves to associate particular smells with sexual reward, and seek out those smells for the rest of their lives. Pfaus was even able to make male rats prefer females that smelled of cadaverine -- eau du rotting corpse. Just pumping the smell into their home cages didn't make them hate it any less, but when it was paired with the only female in the room, they'd get past their disgust to mate with her. And later, when they'd come to associate the reek with sex, half of them would actually select a stinky female over an unscented competitor.

Pfaus believes that humans behave similarly, with neutral and even negative odors becoming positive when we associate them with a current, and past, love.

"We're not talking about pheromones, but odors. Real, honest to God odors that activate the main olfactory system to give you a stimulus. Scent is extremely powerful. You can't tell me how many times you saw the color red yesterday, but smelling the smell of your first boyfriend will present you with a complete memory."

And perfumes, when mixed with the other odors of a partner, will come to smell attractive to you with time. Pfaus's theory would explain why I don't find anything appealing about AXE body spray, which is ostensibly designed to attract me, but suddenly find the smell of laundry soap to be sadly romantic.

It's possible that one day my laundry will just be another chore. Dr. William T. Swaney, who studied pheromones in mice at McGill University in Montreal, hesitates to make such a leap from rodents to humans when it comes to odor conditioning. Sense of smell, he says, just isn't as important for humans as it is for mice.

"If you, as a human, don't have a sense of smell, it doesn't render you behaviorally incapable," he says, "but if you destroyed the sense of smell in a mouse, it wouldn't mate, it wouldn't fight, and it would be completely limited." Humans may change their behavior based on the odors of other people around them, he says, but "the effects are subtle."

"If you meet someone in a bar and they spill your drink on you and insult you," he says, "it's not going to matter how good they smell."

But as far as Pfaus is concerned, when it comes to developing a strong preference for certain odors, we're much the same as the rats he studies -- or he is, anyway.

"Now I know why I like lemon oil," he says, "because all the girls wore it in high school. And even though my high school relationship didn't end on a positive note, that smell makes me seventeen again."

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Rachel Feltman

Rachel Feltman writes about science, technology, and business for Quartz.

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