You may have seen the ads: Just spray a bit of human pheromone on your skin, and you’re guaranteed to land a date. Scientists have long debated whether humans secrete chemicals that alter the behavior of other people. A new study throws more cold water on the idea, finding that two pheromones that proponents have long contended affect human attraction to each other have no such impact on the opposite sex—and indeed experts are divided about whether human pheromones even exist.
The study, published today in Royal Society Open Science, asked heterosexual participants to rate opposite-sex faces on attractiveness while being exposed to two steroids that are putative human pheromones. One is androstadienone (AND), found in male sweat and semen, whereas the second, estratetraenol (EST), is in women’s urine. Researchers also asked participants to judge gender-ambiguous, or “neutral,” faces, created by merging images of men and women together. The authors reasoned that if the steroids were pheromones, female volunteers given AND would see gender-neutral faces as male, and male volunteers given EST would see gender-neutral faces as female. They also theorized that the steroids corresponding to the opposite sex would lead the volunteers to rate opposite sex faces as more attractive.
That didn’t happen. The researchers found no effects of the steroids on any behaviors and concluded that the label of “putative human pheromone” for AND and EST should be dropped.
“I’ve convinced myself that AND and EST are not worth pursuing,” says the study’s lead author, Leigh Simmons, an evolutionary biologist at the University of Western Australia in Crawley.
Simmons belongs to a camp of researchers that believes human pheromones likely exist, but none has yet been identified. He sees AND and EST as an unfortunate distraction, pushed forward in part by science’s “file drawer problem,” which relegates negative results to the laboratory filing cabinet.
A push to publish more negative findings has led to studies like these emerging to question long-held views, says Tristram Wyatt, a pheromone researcher at the University of Oxford in the United Kingdom who was not involved with the work. “It’s an Emperor’s New Clothes kind of moment.”
Yet Wen Zhou, a behavioral psychologist at the Chinese Academy of Sciences in Beijing, contends that AND and EST may well be human pheromones. “My major concern with the experiments in this study is that they were not rigorously designed and conducted,” she wrote in an email to Science. Zhou, who in 2014 published a study finding that AND and EST do indeed influence whether participants judge walking dot figures with “genderless gaits” to be men or women, doubts the faces used were truly “gender neutral.” She’s also concerned that tape used to affix steroid-soaked cotton balls to participants’ faces may have covered up the chemicals.
Martha McClintock, a behavioral neuroscientist at the University of Chicago in Illinois who is widely credited with (and sometimes criticized for) elevating AND and EST to pheromone fame, along with the heavily contested idea that women living together will sync their menstrual cycles, says the findings only really negate an overly simplified view of AND and EST having an almost mystical ability to attract partners. She still thinks the compounds can affect behavior—just in a much more nuanced way than most people think. Her most recent research, for example, has examined how inhaling AND, perhaps from another person’s sweat, might influence someone’s emotions. “There’s no doubt that this compound, even in tiny amounts, affects how the brain functions,” she says.
Wyatt, who is convinced the new work is solid, hopes that investigators will now re-evaluate how they search for human pheromones. Studies focused on sex and attraction are exploring a complicated realm, he says, as human sexual behavior is not well understood. Instead, he argues, scientists should examine babies, who have not developed confounding associations with smells, but seem to respond to pheromonelike substances from any mother’s areola gland secretions, which cause them to stick out their tongue and suckle.