Smell of women's tears may reduce aggression in men: study

Have you ever wondered why someone crying can make the room still? A new study shows that the smell of women's tears can reduce aggression in men.

Researchers found that male aggression reduced by 44% after they smelled women's tears. The study, published in PLOS Biology, found the tears changed brain activity in parts of the brain that connect olfaction and aggression.

The study provides at least one explanation for the long-standing evolutionary puzzle of why we cry — it may serve as a calming mechanism among groups.

Tears contain social signaling chemicals

Studies in mammalian species have shown that tears contain chemicals which serve as social signals, and the effects are very strong.

Male rodent tears contain a chemical that makes females more receptive to sex, or cause pregnant mice to miscarry, if the male's tears are not the father's.

Rodent tears also influence aggression behaviour. Blind mole rats cover themselves in tears to reduce dominant male aggression towards them, while female mice tears contain chemicals that stops male mice fighting. Infant rats also contain chemicals in their tears that reduce aggression towards them — their only line of defense.

What was less clear is how strongly tears can affect aggression in humans. The study authors had previously shown that when men sniffed women's emotional tears it reduced their testosteronelevels and resulted in diminished sexual arousal.

Emotional tears reduced aggression by 44%

This study aimed to test the calming ability of tears. The authors collected "emotional" tears from six female donors, which they exposed to men while they played a video game designed to provoke aggression. In another experiment, the men played the game while in a magnetic resonance imagine (MRI) scanner, which measured their brain activity.

The men displayed 43.7% fewer aggressive behaviors after smelling the women's tears compared to men who smelled a control solution. The brain imaging experiments found that sniffing tears reduced brain activity in regions related to aggression.

"We've shown that tears activate olfactory receptors and that they alter aggression-related brain circuits, significantly reducing aggressive behavior," lead author Joam Sobel, Weizmann's brain sciences department, US, said in a statement.

The authors say the findings mean 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," Sobel said in a statement.

The authors suggest the effect of tears could play an important role in non-verbal communication, for instance in babies.

"Infants can't talk, so for them relying on chemical signals to protect themselves against aggression can be critical," the authors said in a statement.

Gender differences in aggression

The study contributes to a large body of evidence showing how sex and genderplay an important role in human aggression. Sex differences is "one of the most robust and oldest findings in psychology," according to the 2015 international encyclopedia of the social and behavioral sciences.

The study shows how aggressive behaviours can be changed by innate biological cues like the chemicals in tears, at least in men.

The authors aim to extend the research to include women. "We knew that sniffing tears lowers testosterone, and that lowering testosterone has a greater effect on aggression in men than in women.... Now, however, we must extend this research to include women to obtain a fuller picture of this impact," the authors wrote.