© 2024 Gwen Dewar, Ph.D., all rights reserved
Do babies recognize their mothers’ smell? Yes! In fact, body odor is one of the most powerful cues that newborns use to identify their mothers, and – as babies get older – the mere whiff of mom can make them feel safer, and more eager to socialize. When and how do these effects emerge, and how can we use olfactory cues to improve our lives?
The science of smell in newborns
Scientists think it begins during the last trimester of pregnancy: Babies begin to perceive odors, and they learn about the scent of their own, amniotic fluid.
What happens after they are born? Traces of that scent may cling to their bodies, and then get transferred to whatever they touch. Experiments reveal that newborns like the smell, which makes sense. It’s something familiar in an otherwise strange, noisy, bright new world.
So if a baby catches a whiff of amniotic fluid, it will orient itself toward that smell. And not only that, the smell has a calming effect (Larkin 1998). It’s like a chemical road sign that says “this is home, this is safety.”
Researchers have tested the effects of amniotic fluid odors on a number of nonhuman mammals – including rats, mice, rabbits, and sheep. As Peter Hepper argued years ago, the smell of amniotic fluid may help these critters get a head start in recognizing their mothers and (if they are born in litters) their siblings, too (Hepper 1987).
Does the smell of amniotic fluid play a similar role in humans? It would be surprising if it didn’t.
Human newborns show intensified interest in a mother’s breast if it has been dabbed with a bit of amniotic fluid (Varendi et al 1996). And experiments suggest that we can use amniotic fluid to reduce newborn stress.
For example, in one study, full-term newborns cried less when they were exposed to the odor of their own amniotic fluid (Varendi et al 1998).
In another study, investigators used amniotic fluid to dampen down pain and distress in preterm babies who had to undergo a painful procedure (the insertion of a cannula, or needle). When exposed to the smell of their own amniotic fluid, babies showed less pain – and produced less of the stress hormone, cortisol (Alemdar and Tüfekci 2020).
So newborns can benefit from the odor of amniotic fluid. Yet some societies (including Western societies of the 20th century), have favored the practice of bathing infants shortly after birth, which would remove this familiar, comforting odor from the baby’s body.
In recent years, many hospitals have begun to reject this rush to bathe, noting that babies tend to have better health outcomes when bathing is delayed. In part, this is because delayed bathing allows babies to stay warm, and retain the protective, waxy coating on their skin (the vernix caseosa) that safeguards newborns from infections. But perhaps, too, delayed bathing is helpful because it allows the smell of amniotic fluid to linger — jump-starting kin recognition, and encouraging babies to breast feed.
Do newborns have other olfactory preferences?
Yes! Even without the boost of amniotic fluid, newborns show an attraction to the scent of a lactating breast. Within a few days postpartum, babies actively prefer the odors of breastfeeding to the familiar scent of their own amniotic fluid (Schaal et al 2020; Cox et al 2024).
And meanwhile?
Babies seem very quick to identify their mothers by scent of their skin
In one experiment, babies were tested within approximately one day of being born. Researchers presented the babies with two different nightgowns – one previously worn by their mothers, and another derived from an unfamiliar woman who had recently given birth.
Both scents seemed to have a comforting effect on babies. Newborns were more soothed by the odors of the previously-worn nightgowns, compared with the smell of a freshly-laundered gown.
But, nevertheless, the newborns showed a family bias. When presented with their own mother’s body odor, they mouthed more frequently, as if they had learned to associate this particular smell with breastfeeding (Sullivan and Toubas 1998).
How do newborns learn so fast?
Is it possible that mothers smell a bit like their amniotic fluid?
Well, we can’t rule that out. In an experiment, mothers and fathers were able to identify the scent of their baby’s amniotic fluid – telling the difference between their own infant’s fluid, and the fluid of another newborn (Schaal and Marlier 1998).
We also know that babies can recognize the odors of foods that their mothers ate during pregnancy. So unborn babies — during that last trimester — are able to pick out specific odor components that make their way into the amniotic fluid.
So while it’s unclear how much a pregnant mother’s amniotic fluid might resemble her personal body odor, it’s not totally far-fetched to think there is some overlap, and that babies might be capable of detecting this. Maybe some of what’s going on is that babies are recognizing their mothers based on odors they encountered before birth.
However, there is also evidence for a special time window – immediately after birth – when babies are capable of accelerated learning about odors. And this time window might be related to the stress of being born.
In particular, there’s evidence that all the squeezing that newborns experience – during labor contractions – floods their brains with stress hormones, resulting in high levels of alertness. And this might heighten their ability to learn (Schaal et al 2020).
For instance, in a study of babies delivered vaginally, researchers presented some newborns with a new odor very shortly after birth – within 4 to 37 minutes. Other newborns were randomly assigned to encounter the same odor later – 12 hours postpartum.
Both groups received 30 minutes of continuous exposure, after which there was no exposure again until several days later. Then researchers tested to see if babies showed signs of remembering the odor.
The results? Only babies in the early exposure group – who encountered the smell within minutes of birth – showed signs of recognizing the odor later (Romantshik et al 2007).
But what happens if babies skip labor, and are delivered by Caesarean section?
Experiments on rodents suggests that it makes a difference (Miller and Spear 2008), and there is some human evidence too. Human infants born via C- section have failed to show the enhanced postpartum learning effect for odors – unless their Caesarean was initiated after mothers had already experienced some labor contractions (Varendi et al 2002).
So – summing up — newborns are sensitive to odors, and they quickly figure out how to recognize the distinctive nature of their mothers’ scents.
But there’s more. We also know that maternal odors have positive effects on infant behavior.
Mother’s milk soothes newborns in pain
We’ve seen that babies can be soothed by the smell of amniotic fluid. Experiments confirm that the odor of breast milk, too, has a calming effect – reducing distress when babies experience a painful blood draw (Çamur and Erdoğan 2022; Zhang et al 2018). And while newborns can be soothed by the scent of an unfamiliar woman’s breast milk, experiments suggest that the effect is bigger for maternal milk odors (Nishitani et al 2009).
Mother’s body scent prompts older babies (4-to-12-month-olds) to pay more attention to relaxed or happy faces
This is another fascinating finding – documented in a number of experiments on 4-month-old babies. And these studies all depend on the same technique for collecting body odors: Researchers ask mothers to wear the same T-shirt to bed, several nights in a row. Then researchers expose babies to the odors in the T-shirts – while the babies are otherwise separated from their mothers.
If mom isn’t visible, but a baby can smell her, does this have any impact on the baby’s behavior?
To find out, researchers test two conditions: One where babies sit alongside a mother-scented T-shirt, and another (control condition), where babies sit near a clean T-shirt that has never been anywhere near their mothers.
Then babies are presented with things to look at. Like pictures of non-threatening faces. Or images of non-biological objects, such as automobiles.
What happens? Babies are naturally more interested in faces than cars. But when they are exposed to the body odors of their mothers, this bias for looking at faces becomes even stronger (Durand et al 2020). Babies also show greater interest in looking at images of their own mothers, as opposed to the faces of unfamiliar women (Durand et al 2013).
And while this interest is manifested in longer looking times (Rekow et al 2024), it’s also associated with differences in brain activity.
How maternal smells boost baby brain responses to pleasant social cues…and help baby brains “downplay” negative social cues
Researchers can track infant brain activity using painless, noninvasive techniques (for example, by having babies wear an electrode cap that detects electrical signals emanating from the brain). So how do maternal odors affect brain activity during these “look at the faces” tests?
Interestingly, it depends the facial expression. When babies are shown pleasant or emotionally neutral faces, maternal odors appear to intensify brain activity – indicating heightened attention and information processing. But when researchers show babies the faces of people who look frightened, maternal odors appear to have the opposite effect. Baby brains pay less attention, show less evidence of processing information about the fearful faces.
It’s as if smelling mom in the background makes babies feel safer, and therefore less reactive to potentially distressing sights (Jessen 2020).
Maternal odors also appear to help babies experience “brain-to-brain synchrony” with friendly strangers
Brain-to-brain synchrony is a kind of mirroring of brain activity that can occur between two individuals, especially when they are communicating face-to-face: Neurons fire in certain areas of your brain, and my brain begins to respond in a similar way.
As I note elsewhere, experiments suggest that brain-to-brain synchrony is a marker of successful communication. So we can imagine that children will be better off if they can learn to achieve brain-to-brain synchrony with new people – such as a babysitter or caregiving helper. And, as it turns out, experiments show that maternal body odors can give brain-to-brain synchrony a boost.
When 6-month-old babies were exposed to the background scent of their mothers (via a T-shirt), these infants were more likely to experience brain-to-brain synchrony with an unfamiliar, friendly woman. Consistent with the idea that maternal odors make babies feel safe, these infants also showed signs of being happier, and more willing to engage with the stranger (Endevelt-Shapira et al 2021).
What about fathers? Can babies recognize their fathers on the basis of scent?
There’s been very little research addressing this. To date, studies have focused on mothers. But it would be strange and surprising if babies didn’t learn to clock their fathers based on body odor. It’s more of a question about timing. How early in life might babies figure it out?
As you’ll remember, babies appear to be born with an attraction to the odor of a lactating breast, and the act of breastfeeding itself is a major learning opportunity: Babies experience skin-to-skin contact, and lots of exposure to maternal smells.
So we might expect that a parent who breastfeeds is going to have a bigger olfactory impact than a parent who doesn’t – at least in the beginning.
As a result, babies might take longer to learn about the odors of parents who don’t breastfeed – including fathers and mothers who exclusively bottle-feed. In support of this idea, experiments conducted at 2 weeks postpartum have reported that breastfed babies could recognize their mother’s odors, but not their fathers. And bottle-fed babies couldn’t recognize the odors of either parent (Cernoch and Porter 1985).
But there is no doubt that babies will eventually learn to identify the smells of the folks who love and care for them – regardless of whether they are caregivers who breastfeed.
How can we use this information to make life better?
There are many practical takeaways, I think. Here are the biggest ones I see.
1. Don’t go overboard with washing and hyper-grooming.
As noted above, there are several good reasons not to bathe newborns right away. Olfactory learning can be added to this list of reasons.
2. We can help babies soothe themselves by exposing them to our body odors.
We need to be mindful of safety considerations. When a young infant is left in a crib or bassinet or cot, there shouldn’t be any loose bedding or toys or other materials – these can increase the risk of SIDS.
But I can think of safe ways to introduce parental odors to a baby’s nighttime environment. What if, for instance, a parent sleeps with an infant’s pajamas, and then the baby wears these pajamas on a subsequent night? It could be a way to “wrap” the baby in the calming parental scent.
As babies get older, we can try similar things with their favorite blankets or soft toys.
3. When it’s time for our babies to experience new people or places, we may help them cope by providing them with the familiar scents of their parents.
Babies don’t need to venture into these new experiences with nothing more than their own, freshly-laundered clothing. They can bring comforting, family odors with them.
Is this a tested, scientifically proven strategy for better social or emotional outcomes? Not really. Not yet. And in fact when Kirsten Illingsworth investigated this tactic as a way to help infants fall asleep while in daycare, she found that maternal odors didn’t make a difference (Illingsworth 2012).
But while the power of scent may not be enough to help babies sleep in unfamiliar environments, there is still reason to think it can be helpful in other situations.
The experiment mentioned above – where babies met strangers and fell into “brain sync” with them – is a good example. And intriguing experiments on older children suggest that kids with autism experienced cognitive enhancements when they are exposed to the scent of their mothers (Parma et al 2013; Parma et al 2014).
So, yes – babies can recognize the smells of their caregivers, and these odors can help babies regulate their emotions and learn!
Now that you’re here…
If you enjoyed this article, you might enjoy some other, related articles I’ve written, including these:
References: Babies recognize their mothers’ smell
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Title image of newborn on mother’s chest, nose against her skin, by FroggyFrogg / istock
image of father holding newborn in blanket, with mother recovering in the background by szefei / shutterstock
image of father kissing newborn’s hand by Anatta_Tan / shutterstock