Catching a whiff of that delightful “baby smell” on a newborn’s head turns out to have a very practical purpose.

A volatile organic compound, hexadecanal (HEX), is the major component of this scent. This “chemosignal” triggers mothers to be more aggressive and fathers less aggressive, according to a study published in Science Advances by researchers from the Azrieli National Center for Brain Imaging and Research at the Weizmann Institute of Science in Israel.

It seems this cute aggression effect is beneficial for all kinds of mammal babies, as the mother is primed to protect the newborn and the father less inclined to act aggressively toward his offspring.

To test this “sex-specific social chemosignaling” phenomenon, the scientists– led by Eva Mishor from Prof. Noam Sobel’s research group — asked 67 men and 60 women aged 21 to 34 to sniff a mineral oil. Half of them received oil that had HEX added to it.

Weizmann Institute scientists Dr. Eva Mishor and Prof. Noam Sobel. Photo courtesy of Weizmann Institute

The results of the double-blind trial surprised the researchers, who’d expected it to reduce aggression in both genders.

Instead, it had markedly different effects in men and women, quantified in a computerized game that tested their aggressiveness level. Three separate analyses confirmed their findings.

Brain scans further confirmed that while both men and women perceive HEX as odorless, it triggers distinct, gender-related neurological reactions, increasing activity in a brain area implicated in the perception of social cues.

“Babies cannot communicate through language, so chemical communication is very important for them,” explained Sobel. “As a baby, it is in your interest to make your mom more aggressive and reduce aggressiveness in your dad.”

He added that this study is among the first to provide a direct link between human behavior and a single molecule picked up through the sense of smell.