A father’s scent helps babies synchronize their brains with new adults

The scent of a father can help babies synchronize their brain activity with unfamiliar adults and encourage more energetic social play. By simply smelling their father’s body odor, infants essentially invoke his presence, allowing them to form stronger neural connections with strangers. These findings were published in the journal Science Advances.

When two people interact socially, their brain waves often align or pulse in harmony. This mechanism, known as interbrain synchrony, helps infants tune their developing brains to their social environment. It allows caregivers to provide sensory inputs that guide the maturation of the child’s social brain.

Past research has shown that maternal body odors can calm infants and increase their neural synchrony with unfamiliar adults. Maternal scents act as an evolutionary signal of safety, helping infants orient toward faces and reducing their neural responses to fearful faces.

However, the impact of a father’s scent on infant brain development has remained largely unexplored. Paternal interactions typically involve different behavioral rhythms than maternal care. Fathers often engage in more high-energy play, which stimulates positive arousal and encourages infants to explore their surroundings. These interactions help children acquire attentive and cognitive skills, opening them up to the broader social world.

Yaara Endevelt-Shapira, a researcher at Reichman University in Israel and the University of Washington, along with Linoy Schwartz and Ruth Feldman, wanted to investigate how infants respond to their father’s smell. They aimed to determine if paternal body odors act as a sensory signal that helps infants build neural connections with people outside their immediate family.

The researchers conducted a small study involving 40 infants, aged five to twelve months, and their biological fathers. To collect the scent, fathers wore a 100 percent cotton t-shirt for two consecutive nights. They were instructed to avoid scented soaps, shampoos, and deodorants, and to refrain from eating foods that heavily alter body odor.

During the laboratory experiment, the researchers used dual-electroencephalography (EEG) to measure the brain waves of both the infants and the adults simultaneously. EEG is a non-invasive method that uses small sensors placed on the scalp to detect electrical activity in the brain. Connecting both participants to the same amplifier guaranteed that the neural recordings were synchronized down to the millisecond.

First, the researchers compared the infants interacting with their own fathers against interactions with an unfamiliar male experimenter. No toys or physical contact were allowed during these three-minute sessions.

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The infants displayed higher interbrain synchrony with their own fathers than with the stranger. This synchronization occurred specifically in the alpha frequency band, a type of brain wave that develops during the second half of the first year of life. In infants, alpha oscillations are associated with attention regulation, working memory, and visual processing.

The neural connection linked the father’s left central brain region, which handles sensorimotor processing and skill execution, with the infant’s right temporal region. The right temporal cortex is a core area for processing social information, including biological motion detection and attention.

Next, the researchers tested how the father’s scent altered the infant’s interaction with the unfamiliar male. The infants engaged in two sequential interactions with the stranger. In one session, the t-shirt carrying the father’s body odor was placed near the infant. In the other session, a blank, unworn t-shirt was used as a control.

When the father’s scent was present, the neural synchrony between the infant and the stranger increased. The alignment in the alpha frequency band matched the pattern observed when the infants interacted with their actual fathers. When comparing the neural coupling during the odor condition to the synchrony shared between the infant and their real father, the differences were not statistically significant.

The researchers also analyzed video recordings of the interactions to look for behavioral changes. During the sessions with the stranger, the presence of the father’s scent elevated the infant’s positive arousal. This was measured by instances of smiling, laughing, cooing, and changes in posture such as leaning forward or backward.

While overall visual attention and feelings of safety did not increase universally among the infants, the researchers noticed a correlational trend. Infants who looked more at the stranger’s face and displayed more engagement behaviors experienced a larger boost in neural synchrony.

The researchers also surveyed the fathers about their routine involvement in childcare at home. Infants of fathers who reported higher levels of daily involvement showed a more pronounced increase in neural synchrony when exposed to the paternal odor.

Caregiving behaviors are highly variable and do not strictly align with biological sex. Differences observed between this study on fathers and previous research on mothers might reflect individual parenting styles, parental mental states, or varying levels of childcare involvement.

The infants’ ages spanned a period when alpha brain waves are still maturing. This age-related developmental variation could influence the observed neural patterns. Future studies focusing on a narrower age range could clarify how this specific brain rhythm matures over the first year of life.

The experimental design compared the father’s scent to a blank shirt. This leaves open the possibility that infants were reacting to a general human scent rather than their specific father’s odor, though the stranger’s own scent was present during both conditions.

Additionally, the continuous presence of the scent could lead to olfactory habituation, where the infant stops noticing the smell over time. While the researchers found no neural or behavioral differences between the first and second minutes of the interaction, they acknowledge that capturing dynamic changes in brain activity might require more precise odor delivery methods in the future.

Future research could measure the emotional state of the fathers during the odor collection period, as stress or mood might alter the chemical composition of the scent. Investigating populations with developmental differences, such as infants with a higher likelihood of autism, could reveal whether socially relevant scents might assist in building interpersonal neural connections.

The study, “Scent of a father: Paternal body odors boost interbrain synchrony,” was authored by Yaara Endevelt-Shapira, Linoy Schwartz, and Ruth Feldman.