By Lydia Denworth

Copyright scientificamerican

This article was made possible by the support of Yakult and produced independently by Scientific American’s board of editors.

We got our first dog when my oldest son was 10. A friend who was a teacher told me that was a perfect age for a kid to have a pet. “Jake can throw his arms around the dog when he doesn’t feel comfortable hugging you anymore,” he said.

It took a bit for me to get over his reminder that my child was growing up, but I immediately recognized my friend’s insight. A beloved animal can make everything seem better. And most of us believe strongly that our pets make us healthier.

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Yet the science of human-animal interaction has found mixed results when it comes to physical and psychological health benefits from pets. Depending on the study, for example, people with pets are either less or more likely to be depressed. Experts say this seesawing probably happens because, for some owners, pets serve as a calming influence and emotional support. But in other cases, the study may include more people who are already struggling mentally and get pets to try to feel better; then such participants are counted as depressed.

Owning a dog has consistently been associated with higher levels of physical activity, no doubt because of all that walking, which has social benefits, too. One of the very first studies in the field, published in 1980, found that people who had been hospitalized for a heart attack or coronary artery disease were more likely to survive the following year if they had a pet, and the researchers suspected that physical activity from walking dogs was partly responsible, although the results held for other kinds of pets, too. A 2019 analysis of several studies, published in Circulation: Cardiovascular Quality and Outcomes, showed a dramatic result: dog ownership was associated with a 24 percent lower risk of dying. But when other researchers reran the same numbers with more adjustments for confounding variables, that benefit nearly disappeared.

“Pets are not a medical intervention; they’re a relationship.” —Jessica Bibbo, gerontologist

A history of physical activity is one potential confounder. “You’re more likely to have a dog if you’re already somebody who’s active or wants to be active,” says developmental psychologist Megan Mueller of the Cummings School of Veterinary Medicine at Tufts University. “And then once you have that dog, they probably help motivate you to be more active.”

That’s why much of the latest research aims to get beyond such problems by digging into the nuances of human-animal interactions. “Pets are not a medical intervention; they’re a relationship,” says Jessica Bibbo, a gerontologist at the Benjamin Rose Institute on Aging in Cleveland who studies human-animal interactions. And the quality of that relationship, such as the level of attachment and sense of social support, looks like a much better predictor of positive outcomes than just whether there’s a pet in the home, Mueller says: “We are trying to isolate the factors that can help promote those positive relationships [with pets] so we can help people.”

Carefully randomized controlled trials with therapy animals and laboratory experiments offer some clues. A 2025 study had 43 dog owners perform stressful tasks (such as public speaking) with or without their pets present. Those whose dogs accompanied them showed lower spikes of cortisol, a hormone that rises under stress. Another study of about 90 older adults attending a community center randomly assigned half the people to look after five crickets (yes, crickets!) in cages for eight weeks. All the people received the same advice about maintaining their own health. Those who cared for insects showed some improvement in mental and cognitive health compared with those who didn’t.

For older adults, having a pet to care for adds a sense of purpose, Bibbo says, particularly when health is in decline. As part of their work, Bibbo is trying to build pet care into decisions about health care. People often take better care of themselves so they can also look after a loved animal, Bibbo says.

Some of the positive effects seen in controlled settings—such as reduced cortisol levels and heart rates—probably carry over to having a pet in real life, Mueller says, even though real life is messier. As with human relationships, strong, positive bonds with an animal seem to be some of the things that confer health benefits (although even here there are mixed results). Certainly pets provide social and emotional support for many people. There’s a physical component as well from having a cat or dog sit in your lap. As a bonus, pets are viewed as nonjudgmental. “Pets aren’t giving you any tough love,” Mueller says.

For adolescents, that can be especially useful (my friend was right). Pets serve as “a bridge helping young people in their transition to autonomy,” says Mueller, whose work focuses on that age group.

Still, we shouldn’t ask too much. Even therapy animals are there to facilitate, not to fix, Bibbo says. And we can’t expect pets to cure serious mental health issues, Mueller says. “But can having a dog or any pet help us build coping skills that are positive for managing anxiety?” she asks. Mueller thinks it’s very possible.

People emphatically believe pets improve our quality of life, and that belief can affect health indirectly. In 2025 economists used a large British dataset with controlled variables to assess how much more money pet owners thought they would have to earn to get the same life satisfaction that pets gave them. The conclusion: up to $90,000 a year. That’s enough to buy dozens of treadmills or go on many relaxing tropical vacations. Co-author Adelina Gschwandtner of the University of Kent in England says: “Are pets good for us? We were able to answer with a resounding yes.”