Baby smell blocks aggression in men but triggers it in women

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Born yesterday and already starting drama.

A new study has found that a scent given off by newborns causes a surprisingly gendered response.

According to research led by scientists at Israel’s Weizmann Institute of Science, the human-made molecule hexadecanal (HEX) — which is found in large amounts on baby scalps — triggers aggression in women while blocking it in men. The findings were published this month in the journal Science Advances.

“We found that HEX has no perceptible odor, but that when you sniff it, it affects the way you behave toward others — specifically, your aggressive responses to others,” Dr. Eva Mishor, who led the study, said in a press release.

To determine this, the researchers exposed about half of the study’s 130 participants to HEX while the rest received a control. They then gave the test subjects the option to blast a game partner with unpleasant noises of varying intensity. While women exposed to HEX consistently went for the loudest and most unpleasant noises, men who were exposed to HEX consistently chose milder noises than their non-HEX-exposed counterparts.

While perhaps an unintuitive finding based on societal gender norms, Mishor asserted that sex differentiation has an evolutionary explanation.

“Male aggression translates many times into aggression toward newborns; infanticide is a very real phenomenon in the animal kingdom. Meanwhile, female aggression usually translates into defending offspring,” she said. “HEX, it would seem, affects men in that there was more social regulation, their aggression was kept in check and it served as a ‘cool down’ signal for them, while in women the regulation decreased and it can be thought of as a ‘set free’ signal.”

The molecular mind response is, in a way, babies’ evolutionary strategy of communicating with their parents to increase their odds of survival. “Babies cannot communicate through language, so chemical communication is very important for them,” said Professor Noam Sobel, whose research group led the study. “As a baby, it is in your interest to make your mom more aggressive and reduce aggressiveness in your dad.”

In addition to the finding that the scent of HEX affects men differently than it does women, the study is “among the first” to demonstrate a direct link between a molecule’s smell and human behavior. 

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