Archaeological records suggest we’ve been close with our pets for some time: About 10,000 years ago we started to co-habitate with cats drawn to the well-fed rodents scurrying around our farms. In ancient Egypt millions of pet dogs were buried in elaborate tombs adorned with expensive gifts and inscriptions. As a result, we’ve likely been swapping cuddles and microbial critters with domesticated animals for many generations.

Today those pets are clearly still at home in our homes. And plenty of headlines tout that beyond snuggles and companionship our four-legged friends offer other benefits—like improved mental and physical health.

But not so fast. A rash of recent research presents a more muddled picture of what pets bring into our lives—from microbe swaps that can alter our gut environment to emotional well-being. Just consider the family dog: Fresh from a romp through the woods or an inquisitive sniff of a butt or two, he will impart a nip, nuzzle or slobbery smooch—perhaps transferring legion microbes with each encounter. Current science suggests that might be a good thing—but only for some of us.

First, let’s talk allergies. Numerous works tell us that having a dog appears to reduce rates of pet allergies if first exposure takes place very early in life. Many microbiome researchers believe those exposures to pets’ microbial milieu during infancy—in the form of pet dander—may specifically train the immune system to deal with pets and other allergens. (The theory goes: without those early exposures to certain bugs and infectious agents the natural development of the immune system is essentially stunted.) But as one May 2017 study of thousands of kids and adults concludes, the timing of such exposures appears to be key: When first pet exposures occur as a teen or young adult, risk of pet allergy actually appears to increase.

There’s more bad news: Pets can also cause other problems. Lizards and turtles can carry salmonella. Parrots can carry the causative agent of psittacosis—which causes severe pneumonia in humans. And evidence has accrued that many of our furry friends can carry serious infectious agents including “superbug” MRSA, giardia, and other pathogens and parasites.

Even our modern understanding about the mental health benefits from pet ownership continues to evolve. For many decades there was widespread acceptance about the mental health benefits of unwinding with a pet. But that picture was complicated by a 2010 study of nearly 40,000 people in Sweden that found pet owners were physically healthier than those without pets yet they suffered from more mental health problems than their sans-pet peers. Now the science remains unsettled about who may benefit from pet ownership or even why such relationships could help.

We do know pets help us get outside to play or walk them, which increases physical activity. Some of these positive effects may be mediated by microbiome changes in response to decreased cortisol levels, but scientists are still looking for definitive answers, says Rob Knight, who studies these questions at the University of California, San Diego.

What about other physical health benefits? Several research groups are looking into that now. In one ongoing study Knight and collaborators have asked 17 lucky senior citizens to agree to be randomized to receive a dog or not. Then they (and the dogs) submit to months of regular health checkups and share their poop with researchers who map out its microbial makeup. Knight’s group plans to have some results from this study in the next year.

Meanwhile other research groups are also looking for connections between pet ownership and obesity—exploring if certain microbial swaps might help or hurt the midlines of pets and people. Current evidence actually suggests heavier people have heavier pets—a puzzling phenomenon, which some scientists believe could be due to microbial swaps that go in the person-to-pooch direction. It may sound far-fetched but there are some early hints that “fat” microbe transfers are possible: Studies in the past few years do suggest we can make mice fatter or thinner by transferring microbes from fatter or thinner people to them.

Personally, though, right now I’m not counting on any big benefits from pet ownership except looking into those adorable puppy eyes. For me, that’s enough.