Smiling At Babies Could Help Emotional Regulation Develop

THURSDAY, Oct. 1, 2026 (HealthDay News) — The smiles that pass between babies and their caregivers aren't just fleeting pleasures: They might help infants learn how to regulate their emotions, according to two new studies.

One study found that heart rhythms thought to reflect emotional regulation occur only when a baby and their caregiver smile at each other, not when a baby smiles on their own.

The shared smiles impact babies on a physiological level, which then helps emotional regulation develop, explained study senior author Daniel Messinger. He is a professor of psychology at the University of Miami.

For the first study, Messinger's team attached electrodes to the chests and tummies of nearly 1,000 4-month-olds. The researchers tracked infant heart rates as each baby interacted positively with its mother.

The team knew that increases in what's known as "respiratory sinus arrhythmia" — a type of heart-rate variability associated with breathing — is tied to emotional regulation and a person's adaptability to different environments.

Tracking baby-mom interactions, researchers discovered that increases in this type of heart-rate variability only occurred when baby and mom smiled at each other at the same time.

The heart rate change never occurred when mom smiled, but her baby didn't reciprocate, or vice versa, Messinger's team found.

“They both have to be positive,” Messinger explained. “When they’re both positive, particularly for longer periods of time, you see this increase in the baby’s heart rate.”

To Messinger, this suggests that "play is not just fun and games. It’s influencing the baby’s physiology. There’s something about positive sociality that’s associated with this internal baby state. The baby’s physiology is linked to what’s going on in the interaction.”

In a second "smile study," Messinger and colleagues observed 58 infants at ages 4 and 8 months as they interacted with their mothers, their fathers and a stranger.

Overall, adults were more likely to initiate smiling episodes than babies, who smiled more when an adult first smiled at them.

Babies were also typically the first to stop smiling during these shared smiling moments, researchers said.

One thing changed with age, however: By 8 months of age, babies became more likely to initiate a "smiling moment" and to reciprocate an adult's smile than they were at 4 months, the study found.

So, baby-adult pairs become "more dynamically responsive to one another at older ages,” Messinger said in a university news release.

One other finding: Babies were more prone to smiling back at mom than to dad or a stranger.

“This was, importantly, the first paper that involved not only moms and dads, but also strangers,” Messinger said. “The strangers initiate and sustain smiles more than moms, but infants are more likely to smile back at the mom. So, the relationship really counts there.”

Both studies were published Sept. 24 in the journal Philosophical Transactions of the Royal Society B.

More information

Find out more about infant developmental milestones at Johns Hopkins Medicine.

SOURCE: University of Miami, news release, Sept. 29, 2026