Men tend to hate it when women cry — for reasons that they often have difficulty articulating. Now, new research suggests why — men may be biologically primed to react to a woman’s tears. According to a new study, even a whiff of these tears can dramatically reduce men’s testosterone levels and to a lesser extent, their sense of sexual arousal. With or without conscious awareness, women’s crying can just turn men off. (More on Time.com: An Evolutionary Explanation for Altruism: Girls Find It Sexy)
The paper—published in today’s issue of Science—was originally designed to look for general emotional responses to the scent of tears. In mice, fluids similar to tears are used to send chemical signals. For example, male mice become more aggressive when exposed to these fluids from other males. In humans, sexual attraction and the menstrual cycle are known to be influenced by odors.
Researchers initially sought effects on empathy and emotion. “That’s what the study was designed originally to uncover,” says co-author Noam Sobel, professor of neurobiology at Israel’s Weizmann Institute of Science. “Fortuitously, we discovered that what [women’s tears] did influence was sexual arousal. [Tears] had no influence on empathy or sadness, at least in our paradigm.”
The reduction in sexual arousal was discovered because the men in the study had been asked to rate their emotional responses on a widely-used questionnaire that included a question on libido. Says Sobel, “If you look at the self-rating information, [the effect on arousal] was not dramatic but quite consistent.” And it wasn’t seen in all participants: 17 of the 24 men in that experiment reported reduced sexual interest.
“That said, the physiological data told a more compelling story,” says Sobel, explaining that the effect on testosterone was “pronounced” and “almost large enough to be considered reasonable” for an effective drug. Lowered testosterone is linked with lower sexual drive— which is why testosterone patches are used to treat the condition in men and why “chemical castration” (which cuts testosterone) is sometimes used for sex offenders. (More on Time.com: What the U.S. Can Learn from Holland About Teen Sex)
Researchers have not yet isolated the component of tears responsible for the response—but they are actively seeking the chemical.
Charles Wysocki, a behavioral neuroscientist at the nonprofit Monell Chemical Senses Center in Philadelphia, was not associated with the study and calls the research “well done,” saying that the design was “elegant.” He adds, “This suggests that there is a very real possibility that tears may be playing a role in chemical communication in humans.”
The paper raises many intriguing questions: for example, could a drug eventually be developed for use on sex offenders to reduce the likelihood they would commit more sex crimes, including rape? Sobel thinks not. “Even if we would discover a miracle molecule [devised from tears with this effect], I suspect that molecule would have lots of uses in medicine, but I don’t think it would be an anti-rape spray.”
That’s because not all men report reductions in arousal—and given the fact that some people find violent pornography exciting, it could actually exacerbate the problem. “Some men may be immune and even worse, the idea that it could lead them wrong is a viable possibility,” says Sobel. (More on Time.com: Too Many One-Night Stands? Blame Your Genes)
In fact, there are many situations in which the associations a particular person makes between a scent and their experience determine their reaction to that scent. “If for the first time, [someone] smelled roses a a summer walk through a garden with [his] mother, [his response to roses] will be much different than a for child whose first experiences with roses was at the funeral of their mother,” says Wysocki. Childhood abuse by caregivers could potentially affect these kinds of scent-related associations.
For the study, researchers conducted several different experiments. First, they recruited people who could cry tears of sadness at will— prior research has found that tears that simply cleanse the eyes do not contain the same chemicals as emotional tears. Not surprisingly, virtually all of the donors were women. This is why the researchers decided to start by studying male responses to females rather than the other way around. They ultimately want to study reactions across gender to tears from men, women and children.
Once the tears were collected, they were placed in a jar that participants then sniffed. To keep the men exposed to the scent, scientists taped a pad containing the solution under their noses during the rest of the research. 24 men were studied in the first experiment, which involved simply rating their emotional responses to the smell and to pictures of women. Participants were alternately were exposed to tears or saline solution.
Although men couldn’t consciously distinguish between tears and saline—and they were not told that the scent they might sniff could contain tears— they found the women’s pictures less attractive when they had smelled real tears.
Even after watching either a sad or arousing movie scene, only the men who had sniffed the tears reported the same dip in arousal. Physiologically, however, their testosterone, measured in saliva, went down while skin conductance—a measure of electrical activity on the skin linked with emotional changes—increased. So it wasn’t that they weren’t moved by the scences—they simply weren’t turned on. (More on Time.com: Why Neurotic People Need More Sex)
Why might women have a signal in their tears that cuts men’s arousal? Aside from possibly reducing the risk of rape, such a signal could be used to dispel unwanted sex when women aren’t ovulating. “Women cry much more during menstruation,” notes Sobel, “Which indeed from an evolutionary standpoint is not a beneficial time for sexual interaction.”
And this study into the relationship between odors and sexual arousal only hints at a rich area of research that could enhance understanding of sexual orientation as well. Earlier work by Wysocki and his colleagues has found differences in odor preferences related to sexual orientation, with lesbians and heterosexual women tending to find the odor of gay men less attractive than that of straight men, while gay men prefer the whiff of other homosexual men. “We’re just scratching the surface in our understanding of different forms of chemical communication among people,” he says.