Being around animals feels good. From pups to kittens, to horses and pigs, the mental health benefits of being around furry friends are well documented; therapy animals, for example, are often deployed to help people cope with stress. But as a new Proceedings of the National Academy of Sciences study shows, animals don’t just relieve stress in the short term. Being around animals at a young age, the study authors report, seems to provide a mental health boost much later in life.

In the paper, the researchers from University of Ulm in Germany and the University of Colorado Boulder showed that adults who were raised among pets seemed to have a far smaller physiological stress response than people who had a pet-free childhood. What makes this study so interesting is its focus on the physical manifestation of stress: The authors specifically looked for molecules in the bloodstream that are linked to the immunological stress response. People who were raised around animals, they write, have less intense immune responses, a quality that appears to make them better able to deal with stress.

Sheep
People who grew up around animals had less intense immune responses to stress.

The study involved 40 males between the ages of 20 and 40 that had grown up in either of two environments: a pet-free home in a city of more than 100,000 people, or on a farm with animals. These unwitting humans were then put through the extremely stressful tasks of giving a public speech and then figuring out a math problem in front of a bunch of stone-faced people. At several points before, during, and after the harrowing experience, the researchers sampled the saliva and blood of the participants to monitor the stress-linked molecules IL-6 and IL-10 in their blood, anticipating that the farm-raised kids would have lower levels of them in general.

According to the “hygiene hypothesis,” people who are exposed as children to more allergen-laden things — animals included — have less reactive immune systems than those who grow up in sterile environments. Generally, you don’t want an overly reactive immune system because it causes exaggerated inflammation, which is in turn linked to many stress-associated mental disorders (as well as physical ones). As the hygiene hypothesis predicted, the people who’d grown up in cities had a “more pronounced increase” in inflammation-linked molecules after the stressful experience than the rural adults, suggesting that that their bodies were not as well-equipped to deal with stress.

The weird part is that the city kids actually reported feeling less stressed than the rural folk did, even though their bodies said otherwise. “This exaggerated inflammatory response, warned study co-author and UC Boulder integrative physiology professor Christopher Lowry, Ph.D. in a statement published Monday, “is like a sleeping giant that they are completely unaware of.”

Larger versions of this study will hammer down the exact relationship between childhood animal exposure and adult stress responses, but in the meantime it probably won’t hurt to spend more time with animals, suggested co-author Stefan Reber, Ph.D., a psychosomatics and psychiatry professor at the University of Ulm, in a statement: “[It] looks as if spending as much time as possible, preferably during upbringing, in environments offering a wide range of microbial exposures has many beneficial effects.”