Ask any new parent and they’ll tell you how their baby smells indescribably pleasant (as long as their diaper has been recently changed). This isn’t just a matter of parents doting over their newborns: “new baby smell” is a real thing and it appears to play an incredibly effective role in building bonds.

In 2019, Japanese scientists studied the chemical makeup of new baby smell by taking samples from the heads of newborns freshly delivered at Hamamatsu University Hospital. They found the smell was down to 37 volatile odor components, but the exact composition varied from baby to baby, suggesting they all had a subtly unique pong.

The odor compounds from the babies differed fairly significantly from amniotic fluid, the liquid that surrounds an unborn baby in the womb, suggesting this was not the prime source of the smell. 

Another theory is that the odor comes from vernix caseosa, the thin layer of waxy white biofilm that coats a newborn’s skin. While this protective film only lasts a few hours after birth, its scent may linger on the skin and hair. 

Whatever its source, it’s clear that new baby smell has a hold on humans. 

Research in the late 1980s found that 90 percent of mothers were able to identify their newborns by smell alone after spending just 10 minutes to an hour with their infant. 

Catching this scent also helps to release a strong dose of feel-good chemicals in the brain. A 2013 study found the smell of babies sparked activity in the dopamine pathways in parts of the brain associated with reward. 

The experiment was carried out on 30 women, half of whom had just given birth and another half without any children, and found those who were mothers had a stronger response. This led the researchers to conclude that the smell might help to encourage early bonding between mothers and their babies. 

“[This] tentative data suggests that certain body odors might act as a catalyst for bonding mechanisms,” the study authors wrote. 

This relationship appears to go both ways, with numerous studies suggesting how babies also have a nose for their mothers. Research on mice has indicated that babies learn the smell of their mother and use it to initiate suckling. Likewise, research on humans has shown that babies responded specifically to their own mother’s odor by increasing mouthing, which shows they are capable of identifying their own mother just by scent.

Fascinatingly, there’s even evidence that unborn babies react differently to various smells and tastes while still in the womb, suggesting that smell-sniffing may play an important role in early life. 

On the other end of the spectrum, studies have shown that people are also surprisingly good at detecting the classic “old-person smell” and determining whether a person is young or old based on just a whiff. Scientists are fairly clueless about the mechanism behind this curious sensory skill, although they have pointed out that "old-person smell” isn't necessarily a nasty odor. Many people, it seems, actually enjoy the smell.