The Science of Pet Ownership Needs a Reality Check

This article was originally published by Undark Magazine.

For more than a decade, in blog posts and scientific papers and public talks, the psychologist Hal Herzog has questioned whether owning pets makes people happier and healthier.

It is a lonely quest, convincing people that puppies and kittens may not actually be terrific for their physical and mental health. “When I talk to people about this,” Herzog told me, “nobody believes me.” A prominent professor at a major public university once described him as “a super curmudgeon” who is, in effect, “trying to prove that apple pie causes cancer.”

As a teenager in New Jersey in the 1960s, Herzog kept dogs and cats, as well as an iguana, a duck, and a boa constrictor. Now a professor emeritus at Western Carolina University, he insists that he’s not out to smear anyone’s furry friends. In a 2012 blog post questioning the so-called pet effect, Herzog included a photo of his cat, Tilly. “She makes my life better,” he wrote. “Please Don’t Blame The Messenger!”

Plenty of people believe that there’s something salubrious about caring for a pet, similar to eating veggies or exercising regularly. But, Herzog argues, the scientific evidence that pets can consistently make people healthier is, at best, inconclusive—and, at worst, has been used to mislead the American public.

Few experts say that Herzog is exactly wrong—at least about the science. Over the past 30 or so years, researchers have published many studies exploring a link between pet ownership and a range of hypothesized benefits, including improved heart health, longer life spans, and lower rates of anxiety and depression.

The results have been mixed. Studies sometimes fail to find any robust link between pets and well-being, and some even find evidence of harm. In many cases, the studies simply can’t determine whether pets cause the observed effect or are simply correlated with it.

Where Herzog and some other experts have concerns is with the way those mixed results have been packaged and sold to the public. Tied up in that critique are pointed questions about the role of industry money on the development of the field—a trend that happens across scientific endeavors, particularly those that don’t garner much attention from federal agencies, philanthropies, and other funding sources.

The pet-care industry has invested millions of dollars in human-animal-interaction research, mostly since the late 2000s. Feel-good findings have been trumpeted by industry press releases and, in turn, have dominated news coverage.

At times, industry figures have even framed pet ownership as a kind of public-health intervention. “Everybody should quit smoking. Everybody should go to the gym. Everybody should eat more fruits and vegetables. And everyone should own a pet,” Steven Feldman, the president of the industry-funded Human Animal Bond Research Institute (HABRI), said in a 2015 podcast interview.

The problem with that kind of argument, Herzog and other experts say, is that it gets ahead of the evidence (also, not every person is equipped to care for a pet). “Most studies,” Herzog says, “do not show the pattern of results that the pet-products industry claims.”

It seems safe to say that most people don’t get a dog in order to marginally lower their odds of developing heart disease. Research on the health benefits of pets falls into a strange family of science that measures the practical health outcomes of things people typically do for decidedly nonpractical reasons, such as get married and have children.

[Read: Pets really can be like human family]

At the same time, there’s evidence—much of it anecdotal—that at least some people are cognizant of the potential health benefits when choosing to get a pet. And the idea makes intuitive sense to many people, who say that their animals are good for their well-being. Concurrently, hospitals and nonprofits have rolled out programs that aim to use therapy dogs and support animals to improve people’s mental health.

James Serpell began studying the pet effect in the early 1980s, as a young animal-behavior researcher. At the time, spending on pets was rising in the United States. But there was little research on people’s relationships with their animals. “Why are we doing this?” Serpell wondered. “What’s it all about?”

In an influential 1991 paper comparing non–pet owners with people who had recently adopted an animal, he supplied crucial data suggesting that new pet owners experienced a measurable reduction in minor health problems. New dog owners also pursued more physical activity, compared with people who had cats or no pets at all.

In the decades since, researchers have published many studies comparing pet owners and non–pet owners. The results are mixed, sometimes pointing toward health benefits, and sometimes not.

Some of that data may reflect the realities of human-animal relationships—which, like any kind of relationship, can vary for all sorts of reasons. “It doesn’t mean that my lived experience or anyone else’s lived experience is wrong,” says Megan Mueller, a human-animal-interaction expert at Tufts University. “What it means is that it’s different for different people.”

For some people, she says, having a pet can bring stressors. The caretaking responsibilities may be too taxing; the pet may exacerbate family tensions or trigger allergies; the owner may be unable to afford pet food or veterinary care.

The results, some experts say, are also muddied by issues with research methods. The problem is that there are differences between the people who choose to own pets and the people who don’t.

“What happens is, we try to compare people with pets to people without pets, and then we say, ‘People with pets have X, Y, and Z differences.’ It actually is a really invalid way of approaching the research question,” says Kerri Rodriguez, who directs the Human-Animal Bond Lab at the University of Arizona. A study finding that pet owners are more likely to be depressed, for example, may be picking up on a real connection. But it could just be that people already experiencing depression are likelier to get pets.

[Read: Cats are not medicine]

Today, Rodriguez mostly studies service animals, especially for veterans at risk for PTSD. In this context, it’s possible to conduct randomized trials—for example, randomly choosing who will get a support animal now, and who will go on a waitlist to get a companion animal later. Some research on service dogs—including a recent controlled, but not randomized, trial that Rodriguez was involved with—has shown clear benefits.

How much those benefits apply to typical pet owners, experts say, is unclear. And it’s hampered by researchers’ inability to conduct randomized trials. (“You can’t randomize people to pet ownership,” Rodriguez says.)

Rodriguez says she’s interested in studies that track the association between human-pet relationships and health over time, checking in with people again and again and collecting larger amounts of data. One such study, for example, found a slower rate of decline in cognitive function among older pet owners.

Serpell, after his 1991 study, largely moved on to other research questions. “I basically concluded that this type of research was too difficult,” he says. “And even if you did it, the results you would get would always be questionable.”

These doubts have not deterred interest in the field from the companies that lead the pet industry, which is today valued globally at more than $300 billion.

Almost from the start, the quest to understand the health effects of pets has been entangled with industry money. Serpell’s earliest work was funded by what is now known as the Waltham Petcare Science Institute, a division of Mars, which owns a portfolio of pet-food and veterinary-care brands in addition to its famous candy business. “There was no other source of funding, really,” recalls Serpell, who’s now an emeritus professor at the University of Pennsylvania. “Nobody else was willing to put money into this field.”

In 2008, Mars entered a partnership with the National Institutes of Health in order to spur more research into the relationship between human-animal interactions. In the first year, the pet-product provider ponied up $250,000, while the federal government supplied $1.75 million. (The NIH partnership ended in 2022, although Mars continues to underwrite research on pets and human health.)

In 2010, a group of pet-industry heavyweights launched HABRI. Key funders have included Petco, Nestlé Purina PetCare, and Zoetis, a veterinary-pharmaceuticals firm. “Pets and animals make the world a better place, and we’re going to use science to prove it,” Feldman, HABRI’s president, said in a 2014 talk at a conference for pet bloggers.

The nonprofit has spent more than $3 million funding research on human-animal interactions. Companies also directly fund university research: One prominent research group at the University of Arizona—separate from Rodriguez’s lab—includes a sponsor page on its website featuring the logos of Nestlé Purina, Waltham, the veterinary drugmaker Elanco, and other pet-product companies.

“Funding from the pet industry has transformed the field, and without it, we would not have the science that we have,” Mueller says. (Like Serpell and Rodriguez, Mueller has received industry funding for some of her research.)

Did that funding shape the field’s findings? “I think it has largely been done in a really ethical way,” Mueller says. She and Rodriguez both say they have never felt pressure to produce a particular result. Waltham, when it entered the partnership with NIH, gave up the right to select who would get the funding. Industry-funded studies have found—and published—results that suggest little benefit from pets.

“I really think that the field has done a good job of publishing a lot of findings that are maybe not what people would expect,” Mueller says.

Herzog says he has seen little evidence that industry money has changed the science. Mostly, he says, “they’ve funded pretty good studies.” But there are ways that industry funding can change the field. “It’s always been a source of great ambivalence, I think, for everybody involved,” Serpell says. “You try and work around it, by getting whoever funds the work to stay off your back and let you do the work, and if they don’t like the results, that probably means the next time you apply to them for funding, you won’t get it.”

Funding can shape the questions that a field asks—or avoids. “Industry-funded studies tend to produce results that favor the sponsor’s interest,” says Marion Nestle, an emeritus professor at New York University who has spent decades studying corporate influence on science. Sponsors influence what gets studied, Nestle says, and they select for studies that they think will produce positive results. And, she says, research suggests that sponsorship can shape the way results are interpreted—often without researchers being aware of the influence at all.

Controlling the focus of the research can also steer scientists away from certain topics entirely. “For obvious reasons, these companies don’t wish to draw attention to the darker side of the human-pet relationship,” Serpell says, referring to research areas such as dog bites. In a recent Zoom interview, Feldman told me that funders “can tell us what kind of things they’re hoping to see,” and the organization will try to accommodate those requests: “But then, once the process of funding a project begins, there’s absolutely no influence there whatsoever.”

[Read: Too many people own dogs]

HABRI embraces negative results, or those that don’t show a clear effect from pet ownership, and not just positive findings, Feldman said. But, he acknowledged, they may choose to emphasize positive results. “We try and be very true to the science, but if we take a slightly more optimistic view as to the body of work than researchers who take a different perspective, I think that helps generate a lot of positive behavior in the real world.”

Herzog, Feldman suggested, was making a name for himself with naysaying—in ways that, perhaps, sometimes defy common sense. A 2021 HABRI survey found that nearly nine in 10 pet owners report that their pets benefit their mental health. “I kind of think pet owners might be onto something,” Feldman said.

Herzog agrees that having a pet can have real benefits. At the end of a recent conversation, he reflected on his cat, Tilly, who died in 2022. She used to watch TV with him in the evenings, and she would curl up on a rocking chair in his basement office while he worked. The benefits of their relationship, Herzog said, were real but perhaps hard to measure—among the intangible qualities that are difficult to capture on research surveys.

“If you’d asked me, ‘Did Tilly improve the quality of your life?,’ I’d say ‘Absolutely,’” he said. “My health? Nah.”