As anyone who’s ever witnessed a handoff to a babysitter or a drop-off on the first day of day care can attest, a hug or a snuggle from a sibling or trusted adult can be instrumental in relieving some of the anxiety, and even panic, associated with the departure of a parent. The research to confirm this goes far beyond anecdotes: According to decades of psychological study, positive touch from adults can not only lower stress levels in the moment but can have long-term beneficial effects if administered regularly. And, relatedly, a consistent lack of positive touch has been shown to have detrimental effects on kids as they mature.

Tiffany Field, a professor of pediatrics, psychology, and psychiatry, founded the Touch Research Institute at the University of Miami’s school of medicine in 1992. In the years since, she’s studied the effects of touch on kids in both traumatic situations (a 1996 study of kids whose families had been affected by Hurricane Andrew found that kids who routinely received back rubs from massage therapists saw significant improvements in their PTSD symptoms) and everyday situations (a 1999 study compared kids in Paris, “who get significantly more physical affection from their parents than kids in Miami,” with their counterparts in Florida and found that the former were less physically and verbally aggressive).

On some level, people know that a caring touch makes them feel calmer. Much of TRI’s work over the past quarter century, though, has focused on what exactly happens in the body when humans are touched by other humans. According to Field, any activity that moves the skin stimulates the pressure receptors underneath it—which in turn increases the activity of the largest cranial nerve, the vagus nerve.

The vagus nerve has pathways to all major organs, Field says. “It slows down the heart. It goes to the GI tract and helps digestion. It helps our emotional expressions—our facial expressions and our vocal expressions. It enhances serotonin, the natural antidepressant in our system,” she says. “So that’s why hugging is good. That’s why massage is good.”

Plus, Field says, skin stimulation and the resulting vagal activity lowers levels of the stress hormone cortisol. High levels of cortisol are linked to a variety of health problems, such as anxiety, depression, cardiovascular disease, digestive problems, headaches, and sleep problems; additionally, elevated cortisol is known to harm the “natural killer cells” that help eliminate viral, bacterial, and cancer cells. In TRI studies, ten-week-old babies whose mothers massaged them regularly were found to get fewer colds and fewer bouts of diarrhea as they grew.

Elevated cortisol is also known to hamper the function of the hippocampus, the part of the brain that facilitates memory and learning; as a 2005 report from the National Association for the Education of Young Children notes, “Children who sustain chronically high cortisol levels demonstrate cognitive, social, and motor delays in greater numbers than children with more normal levels of cortisol.” A 2015 New Yorker story noted that when the researcher Mary Carlson conducted studies in the 1990s of children raised in Romania’s state-sponsored leagăne—institutional homes for small children that were erected to facilitate Nicolae Ceaușescu’s mandated baby boom—she found they reminded her of the socially deprived monkeys and chimpanzees she had studied in the past. The children, who were severely neglected and deprived of sensory and tactile stimulation, were characterized by “muteness, blank facial expressions, social withdrawal, and bizarre stereotypic movements.” They also had markedly elevated cortisol levels in their saliva.