Scientists say the perfect hug is a medium-pressure squeeze for 20 seconds

• Researchers in Japan had parents hug their own babies, as well as others' babies, as an experiment to find the perfect and most soothing hug.
• They found that infants preferred hugs with moderate pressure from their own parents, not strangers.
• Parents also felt more soothed when hugging their babies, suggesting there are benefits for adults too.
• The study highlights just how important human-to-human contact can be for a person's health.

If you've ever wondered what makes a great hug so soothing, researchers at Toho University in Tokyo, Japan now have some insights into the factors that make for a perfect cuddle session.

In the pursuit to study the perfect hug, the researchers recruited Japanese moms and dads (with the exception of one British dad) and their infants. They performed three experiments, one with fathers and their infants, one with mothers and their infants, and one with female strangers and infants.

Each adult would hug their assigned baby for 20 seconds, first with a moderate-pressure squeeze, and then with a tight-pressure one, which were both measured using pressure sensors the parents held in their hands during the hugs.

The researchers would observe how the adults' and infants' ratios of heartbeat intervals changed during the various hugs. Ratios of heartbeat intervals is a measurement that increases when a person's heart rate decreases, so an increased ratio of heartbeat intervals suggests a person or infant is calmed, according to the researchers.

The researchers also used the infants' head movements as measurements for how soothing a particular hug was. The fewer head movements they had during a hug, the more soothed the infant was, researchers wrote.

According to their study, which was published April 7 in the journal Cell Press, the most soothing hugs involved a couple of factors, including a moderate-pressure squeeze, and hugs that came from parents, not strangers.

"Even though infants cannot speak, they recognize their parents through various parenting methods, including hugging, after four months old at latest," study co-author Sachine Yoshida said in a press release. "We hope that knowing how your baby feels while being hugged help ease the physical and psychological workload of taking care of infants too young to speak."

Parents felt soothed just like their babies after giving the 'perfect' hug

The researchers also studied the parents' physiological responses during the hug experiments, and found that when parents hugged their own children at a moderate level of pressure, they also had increased ratios of heartbeat intervals and therefore felt calmed.

In recent months, the coronavirus pandemic has resulted in less contact with others, and therefore less skin-to-skin contact. That long-term lack can result in emotional distress known as "skin hunger," Insider previously reported.

This new study adds to further evidence that human-to-human contact is an important facet of health.

There were some caveats to the study. The researchers said the motion of lifting an infant out of their crib prior to the hug experiment could have affected their ratios of heartbeat intervals and therefore skewed the study's results. The study focused on Japanese parents and their babies as well, so the findings may not be applicable to other populations.

Still, the study's researchers hope their findings help parents realize the power of a great hug, especially when caring for their young children who can't yet vocalize their needs.

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