Smelling women’s tears reduces aggression in men, scientists find

Smelling women’s tears reduces male aggression, scientists have found, in a breakthrough that may help solve the mystery of why humans cry.

Humans and dogs are the only animals that shed tears when overcome with emotion, but scientists such as Charles Darwin believed the release served no useful function.

Now researchers at the Weizmann Institute of Science in Israel have found that tears contain social signals which appear to act as a ‘chemical blanket’ to protect the weeper.

Sniffing for answers

In a series of experiments, men were exposed to either women’s emotional tears or saline, without knowing what they were sniffing nor being able to distinguish between the two, since both are odourless.

Next they were asked to play a game designed to trigger revenge-seeking aggressive behaviour in one player towards another.

The team found that after the men sniffed women’s emotional tears, their revenge-seeking aggression during the game dropped by nearly half – 44 per cent.

Brain scans during the experiments also showed that regions related to aggression were less active while the men were sniffing tears.

And when researchers applied the tears to 62 human olfactory – smell – receptors in a laboratory dish, they found that some were activated.

Tears form ‘chemical blanket’

Professor Noam Sobel, of Weizmann’s Brain Sciences Department, said: “We’ve shown that tears activate olfactory receptors and that they alter aggression-related brain circuits, significantly reducing aggressive behaviour.

“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.”

All land mammals have tear glands in their eyes, but in most other animals it was thought they were only used to keep eyes moist and clean.

Recent studies, however, have shown that tears of female mice contain chemicals that affect aggression networks in the brain of male mice, reducing fighting. Subordinate males of blind mole rats will also smear themselves in tears to reduce a dominant male’s aggressive behaviour towards them.

It was recently also discovered that dogs shed emotional tears, although it is not yet known whether the chemical signals have evolved to be picked up by other dogs or humans.

Reduced testerone

Prof Sobel’s team also previously showed that sniffing women’s emotional tears reduced testosterone levels in men, resulting in diminished levels of sexual arousal.

Doctoral student Shani Agron, of Sobel’s lab, said: “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.

“Now, however, we must extend this research to include women, to obtain a fuller picture of this impact.”

The team believes that the study may also help explain why babies cry so much.

“Infants can’t talk, so for them relying on chemical signals to protect themselves against aggression can be critical,” added Agron.

The research was published in the journal PLOS Biology.