What's four-legged, furry, and often serves up a quick little mood boost?

That's right, a dog. It turns out even short, friendly interactions with canines can be good for our health.

I started pondering the power of dogs during one of my daily strolls around my neighborhood. Almost invariably, I'll run into at least one person walking their dog. If I get the OK to pet the pooch, it's a joyous moment of cooing and sloppy kisses.

I always walk away from these canine exchanges feeling just a bit more relaxed, and happy. And that got me wondering, could these short interactions with other people's dogs actually be good for me?

"Absolutely. I think it is safe to say that animals are beneficial to our mental and physical health," says Nancy Gee, a professor of psychiatry and director of the Center for Human-Animal Interaction at Virginia Commonwealth University.

Gee says evidence is accumulating that levels of the stress hormone cortisol drop in people after just 5 to 20 minutes spent interacting with dogs — even if it's not their pet. "Also, we see increases in oxytocin , that feel-good kind of bonding hormone," she says.

And it's not just humans that benefit from these brief exchanges. "What I love about this research is that it's a two-way street," Gee says. "We see the same thing in the dogs, so the dogs' oxytocin also increases when they interact with a human."

Now, the therapy dogs used in research are screened for things like friendliness, good behavior and responsiveness to their handler's cues. And of course, not everyone's a dog person, whether because of temperament or allergies or other factors. "Pets are not a panacea," Gee says. "They're not necessarily going to be great for every single person. But for people who really get it, who really connect with the animals, they really can make a big difference," Gee says.

Dog ownership has also been linked to positive health outcomes, including better heart health and increased physical activity. But Gee acknowledges that some of the evidence is mixed. She attributes that in part to differences in methodology and the fact that studies of pet ownership can't prove cause and effect, since you can't just randomly assign one person a dog as a pet and another a horse.

Research on the health benefits of human interactions with animals – especially with dogs – has exploded in recent years, thanks to funding from the National Institutes of Health and the Waltham PetCare Science Institute . Though the field is still young, Gee says the quality of the evidence is improving all the time, including more randomized controlled trials looking at short interactions. "We're seeing really nice effects," she says.

For example, there's some evidence that brief bouts of puppy love may help us think better. Gee collaborated on a randomized controlled trial of 8 and 9-year-old school children in the U.K. She and her colleagues found that kids who had twice-weekly, short exchanges with dogs in the classroom had less stress and improved executive functioning – the cognitive processes that allow us to do things like plan, stay on task and block out distractions. And she says those benefits lingered.

"We actually saw [those effects] one month later. And there's some evidence that [they] may exist six months later," Gee says.

So what is it about hanging out with dogs that helps us chill out and focus? Megan Mueller , an associate professor at the Cummings School of Veterinary Medicine at Tufts University, says dogs prompt us to experience the world more like they do.

"Animals, and dogs in particular, live in the moment. They're experiencing their environment with wonder and awe all the time, and they're not bringing up what happened to them earlier in the day or what they're thinking about in the future. They're there right now," says Mueller.

Mueller, whose research focuses on the psychology of human-animal relationships, says watching dogs sniff the grass or explore the world around them cues us to pay more attention, too. "They sort of pull you out of your phone and into whatever environment that you're in."

She says there's some evidence that the act of actually touching a dog might be an important part of their calming effect. For instance, one study done in Canada found that college students reported less stress and reduced feelings of homesickness after brief interactions with dogs, and that effect was much bigger in those who actually got to pet the animals. She's currently running a study that's finding similar results.

"Some of the initial research has shown that physical touch might impact our nervous system in a way that's beneficial," Mueller says.

But it's not just how we cue into dogs that makes the relationship special. Gee of Virginia Commonwealth University says over thousands of years of domestication, dogs have developed a wondrous ability to read us humans.

"They really can connect with another human being. And they do it in a very unassuming way," Gee says.

And they do it without the ability to use words. As my dog-loving 9-year-old recently told me, dogs just have a way of speaking to our hearts.

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