Sniffing Women’s Tears May Reduce Aggression in Men, Study Finds

The findings, which may extend to all humans, suggest emotional tears might serve an evolutionary purpose

close-up of eye and tear on woman's cheek
Human tears may contain an odorless chemical substance that reduces aggression, a new study finds. RunPhoto via Getty Images

Tears often spur feelings of empathy between people. But a recent study shows they may bring about this effect in more ways than one: Sniffing women’s tears may reduce aggression in men, suggesting a protective purpose for the emotional response.

Researchers found that after smelling women’s tears, men experienced reductions in aggression by more than 40 percent, as assessed through levels of aggressive behavior and brain activity. The scientists say this conclusion, published last week in PLOS Biology, may extend to all human tears.

“These findings suggest that tears are a chemical blanket offering protection against aggression—and that this effect is common to rodents and humans, and perhaps to other mammals as well,” co-author Noam Sobel, a neurobiologist at the Weizmann Institute of Science in Israel, says in a statement.

Though limited research has examined the realm of human chemosignaling, Sobel’s lab previously observed that women’s tears lowered men’s testosterone levels, physiological indicators of arousal and self-reported sexual arousal.

“We knew that sniffing tears lowers testosterone and that lowering testosterone has a greater effect on aggression in men than in women, so we began by studying the impact of tears on men, because this gave us higher chances of seeing an effect,” Weizmann Institute neurobiologist Shani Agron, lead author of the study, says in the statement.

Humans can pick up on a whole host of odors and chemicals emitted by other humans that provide social cues, often unconsciously. Previous research suggests people may smell fear and anxiety from others, and evidence supports the idea that sweat can also convey emotional information. Chemical communication between species happens as well: Dogs appear to pick up on human chemosignals indicating different emotions, such as happiness and fear.

To test how tears factor into this, the authors collected “emotional” tears from six female donors ages 22 to 25—the members of this small sample group were the only ones of over 100 volunteers who were able to produce enough tears for the study. Sobel tells Scientific American’s Rachel Nuwer that tear collection proved a big challenge to the team, as they needed to provide at least one milliliter of tears to each male participant, which is “a lot of tears.” Further, the watery droplets could not be induced by methods such as cutting onions, which produce a different kind of tear than is generated by watching sad movies, the method most participants used.

Twenty-five male volunteers then played a video game designed to incite aggression. The participants played against a computer algorithm opponent, but they were led to believe it was a cheating, human player. The scientists measured the men’s aggression by calculating the number of times they chose to take revenge against the opponent. In a second part of the experiment, 26 men played the same game while in a magnetic resonance imaging (MRI) scanner that monitored their brain activity.

In both experiments, the participants sniffed either female tears or a saline solution, both of which are odorless, and were not told what they were inhaling. The men displayed 43.7 percent fewer aggressive behaviors after smelling the women’s tears when compared to the saline control. Further, two brain regions related to aggression and decision-making—the prefrontal cortex and left anterior insula—showed significantly less activity after men smelled the tears, per Scientific American. Connections to the amygdala, a part of the brain responsible for emotions and olfaction, increased as well.

These findings on tears’ social chemosignaling power build on similar phenomena seen in non-human animals: For instance, subordinate male naked mole rats will cover themselves in teary secretions to avoid attacks from dominant males, and the tears of female mice contain a chemical that curtails aggression between male mice.

In future research, the team hopes to examine whether human women display similar reductions in aggression after tear-sniffing and whether babies’ tears could produce a similar response in adults.

“Babies can’t say: ‘Stop being aggressive toward me.’ They are very limited in their ability to communicate, and they are helpless as well. They have a vested interest in lowering aggression and that reflects the sad reality of aggression toward babies,” Sobel says to the Guardian’s Ian Sample.

In reality, however, these chemicals may not have much bearing on interactions between adults, says Minna Lyons, a psychologist at Liverpool John Moores University in England who was not involved in the study, to the Guardian.

“The tears of the target of domestic violence may do little in reducing aggression of the perpetrator. Why does the chemosignaling not work in these circumstances?” she says to the publication. “The social context of crying is massively complicated, and I suspect the reduction of aggression is just one of the many potential functions of tears.”

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