It was revealed through brain waves that a baby recognizes a father's body odor and scent, and can naturally get along with a stranger just from the smell even when the father is not nearby. While the impact of a mother's scent on a baby has been known, the effect of a father's scent was confirmed for the first time in this study.
Researchers led by Professor Ruth Feldman and Dr. Yaara Endevelt-Shapira at the Developmental and Social Neuroscience Lab at Reichman University in Israel said on the 15th (local time) in the international journal Science Advances, "Babies show higher brain synchronization with their fathers than with unfamiliar men, but when the father's body odor is present, synchronization with an unfamiliar man can improve to the level seen with the father."
◇ Inducing brain synchronization with father's scent alone
The sense of smell is the most primal sense for humans. Even without the mother, mammalian young become familiar with their living place and develop their brains through the mother's scent alone. In particular, through Federated Learning, which links simultaneous events or stimuli, they learn how to predict how the world works.
The researchers had previously found that babies feel at ease with strangers when a mother's scent is present. This time, they tested whether a father's scent has the same effect. The study involved 40 father-baby pairs. The babies were 5 to 13 months old.
First, the fathers placed T-shirts they had worn for two days during the experiment into glass jars. To preserve the scent fully, they did not wash or use perfume for two days. Fathers wore caps to measure brain waves and played with their babies while looking at them. The babies also wore brainwave-measuring caps. There was no physical contact; they interacted only with faces, gestures and sounds.
When babies met their fathers, their brain waves meshed closely. That is, interbrain synchronization occurred. It did not occur when they met a stranger. Interbrain synchronization does not mean the two people think the same thoughts. It means their brainwave rhythms align. They adjust their actions in response to each other.
The level of interbrain synchronization between a stranger and a baby was low, but it changed when the father's scent was present. When the T-shirt the father had worn was placed in front of the baby during the experiment, interbrain synchronization with the stranger rose to the father level. Even with just the father's smell, the baby looked at the stranger, gestured and babbled as if playing with the father.
◇ Showing a different effect from mother's scent
Babies are familiar with the mother's smell from the fetal stage. They encounter the father's scent after birth during caregiving. Accordingly, the effects of a mother's scent are well known. In 2021, using a similar experimental design, the researchers found that when clothing carrying the mother's scent is present, babies feel comfortable even with strangers.
The researchers analyzed how the father's and mother's scents differ in interbrain synchronization with babies. When seeing the father or when the father's scent was present, babies smiled more, babbled and moved more, indicating an increase in positive arousal. In contrast, the mother's scent increased looking at the face, positive affect and approach behaviors overall.
The researchers interpreted these results to mean that interaction with mothers lowers babies' tension and arousal and provides stability and familiarity, while fathers raise arousal and promote environmental exploration and challenging play. The mother's scent, familiar from the fetal stage, gives babies comfort, and the father's scent can signal that it is fine to engage in lively play together. Through scent, interbrain synchronization forms a rhythm of safety with mothers and a rhythm of exploration with fathers.
In fact, the more a father regularly participated in childcare, the stronger the effect of his scent in inducing interbrain synchronization between an unfamiliar man and the baby. This supports the possibility that, rather than the scent itself containing a father-specific effect, babies may have learned to consolidate the father's scent with enjoyable interactions through holding, feeding, putting to sleep or playing.
However, it is early to say the difference between the effects of mother's and father's scents has been confirmed, as they were tested at different times. The small sample size is a limitation. The researchers said larger studies that examine the effects of mother's and father's scents simultaneously are needed. Still, the fact remains that it is good for brain development when mothers and fathers spend more time with their babies.
References
Science Advances (2026), DOI: https://doi.org/10.1126/sciadv.aed6110
Science Advances (2021), DOI: https://doi.org/10.1126/sciadv.abg6867