Newborn babies, parents swear, have a distinct smell. According to new research in the journal Frontiers in Psychology, that universal baby smell does not occur by chance but rather is a carefully concocted perfume of biological manipulation, evolved to trigger maternal bonding.

Smells have long been associated with mother-child bonding. Babies can recognize their mother’s smell, past research indicates, and moms likewise can do the same for their children (even their poop). Now, this new paper teases out the mechanisms behind that olfactory bonding, at least on the mother’s end.

Researchers recruited 30 women for their study, 15 who recently gave birth and 15 who did not have any children. They asked the women to try and identify various mystery scents, including the smell of a newborn, taken from a baby’s pajamas. While the women sniffed, the researchers watched their brain activity via fMRI.

Most of the women struggled to pinpoint the baby smell, although they generally said it was a pleasant one. Their brains, however, told a different story. When sniffing the baby pajamas, the dopamine pathways in a region of the brain associated with reward learning lit up, LiveScience reports. Other odors, like those of delicious foods, trigger this pathway, and the same dopamine surge is also associated with satiating sexual and drug-addiction cravings. This mechanism influences us by triggering “the motivation to act in a certain way because of the pleasure associated with a given behavior,” Medical Xpress writes.

Although all the women reacted this way to some extent, the mothers had a much stronger reaction than the non-mothers. “For moms the sensation one gets when sniffing an infant presumably feels even more like the feeling of having obtained food,” Christian Science Monitor writes.

This finding left the researches with a sort of chicken-or-the-egg puzzle, however. LiveScience explains:

The researchers aren’t sure if new moms undergo a hormonal change that leads to this surge of dopamine or if their reaction is influenced by the experience of smelling their own baby, the researchers say. “It is possible that childbirth causes hormonal changes that alter the reward circuit in the caudate nucleus, but it is also possible that experience plays a role,” Frasnelli said in a statement.

The researchers did not test whether or not men also undergo this same dopamine spark when sniffing an infant, though finding that answer would hint at the mechanism behind women’s reactions.

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