Does Having a Dog Change Your Gut Bacteria?

If you type "are dogs good for your" into Google, "gut health" comes up as a suggestion, right next to "immune system." If you type "do dogs make you," one of the suggestions is "sick." Both are fair things to wonder about an animal that licks your face, sleeps on your bed, and puts its nose in things you would never touch.

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For teens and adults, a dog changes the bacteria on your skin a lot more than the bacteria in your gut. The gut studies on grown people mostly found no change in how varied their gut bacteria were, and only small shifts in a few types. Babies are a different case, and most of the research that makes dogs sound good for your gut is about them.

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Where the sharing shows up

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Most of the stories about dogs sharing their bacteria with you trace back to a 2013 study in eLife that sampled the skin, mouths, and poop of 159 people from 60 families. People who lived together shared more bacteria than strangers did, and dogs added to that on the skin: adults who owned dogs tended to have more varied bacteria on their skin (hands and forehead). In the gut and mouth, the researchers wrote, they didn't detect any effects of gender or dogs.

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A 2025 study of 345 teenagers in Tokyo looked at the mouth again and found a little more. Dog owners had more of twelve types of mouth bacteria, although the overall variety of bacteria in their saliva was similar between the groups. The same study also looked at the teens' mental health, which is a separate question from this one (see whether gut bacteria can affect your mood).

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What happens when an adult gets a dog

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If you want to know whether a dog changes someone's gut, the cleanest way to check is to sample the same people before and after the dog arrives. A 2024 study in Japan did that with 28 people and their new dogs, testing everyone's poop before they moved in together and again at two weeks, one month, and three months. Some bacteria did cross over (the researchers found 11 exact matches shared inside of human-dog pairs), but the humans' gut microbiome didn't change over time once they were living with the dogs. The dogs' gut bacteria changed significantly in the first month.

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Studies that compare owners with non-owners at a single point in time mostly land in the same place. One in Wisconsin tested 332 adults, 178 of them living with a pet, and found no difference in how varied their gut bacteria were. Its authors concluded that owning a pet likely has little impact on the makeup of an adult's gut microbiota. A few types of bacteria were more or less common in the pet owners, but the pet owners were also about ten years younger (a median age of 53, versus 63), so the researchers had to adjust for age before they could compare the two groups fairly.

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In the Czech Republic, researchers tested 118 adults and set having a dog against where people lived. Owning a dog "had no significant effect" on how varied their gut bacteria were, but living in a village instead of a city did.

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The study that found the biggest difference in adults looked at 54 dog owners over 65. Their overall variety of gut bacteria wasn't different either, although a few families of bacteria were more or less common than in non-owners, and the authors wrote that the benefits they saw still need to be confirmed in a larger group of people. The data came from people who had mailed their own samples to a crowdsourced gut-testing project.

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What about babies?

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A baby's gut bacteria are still settling in over the first year (more on that in are you born with your microbiome), which leaves more room for a dog to make a difference. The biggest study on this looked at 746 babies from a Canadian study that followed kids from before birth. Babies who lived with a furry pet, both while their mom was pregnant and after they were born, were more than twice as likely to have high levels of two bacteria, Ruminococcus and Oscillospira, at around three months old.

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Those two bacteria have been "negatively associated with childhood atopy and obesity" in earlier research, which means that kids with more of them have tended to have fewer allergic conditions (atopy is the tendency to develop things like eczema, hay fever, and asthma) and less obesity. The Canadian study only measured the bacteria, though, so it can't say whether the babies with dogs actually ended up with fewer allergies.

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An earlier, smaller study of 24 babies from the same Canadian project had flagged its own problem, with its authors writing that the main limitation of the study was its sample size. Babies with pets tended to have a richer and more diverse microbiota, but the difference was small enough that it could have been chance.

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Do dogs prevent allergies?

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Allergies are why the baby research gets so much attention, and the results for actual allergies are a lot less clear than the results for bacteria. A combined analysis of 11 European studies, which followed more than 22,000 children from birth, found that having a pet early in life didn't appear to either raise or lower the risk of asthma or allergic rhinitis symptoms in children aged 6 to 10 (allergic rhinitis is hay fever). Its authors told doctors that they shouldn't give advice either to avoid pets or to specifically get them in order to prevent asthma or hay fever.

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Germany's official allergy-prevention guideline, written by the country's allergy and pediatric societies, doesn't tell anyone to get a dog either. It says only that even families with a high risk of allergies "should not be advised against keeping dogs."

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The Crohn's study

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A Canadian study tied growing up with a dog to a lower risk of Crohn's disease (a type of inflammatory bowel disease, where the immune system attacks the gut). The researchers followed 4,289 healthy parents, siblings, and children of people with Crohn's, half of them 17 or younger when they joined. Over about five and a half years, 86 of them developed Crohn's. The people who had lived with a dog between ages 5 and 15 had a 38% lower risk. They also had more varied gut bacteria and did better on a urine test that measures how much gets through the gut lining (the thing people call leaky gut).

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In the press release for the study, its senior researcher, Williams Turpin, pointed out that the pet history came from questionnaires, so the results should be interpreted with caution because of possible recall bias (people misremembering their childhood). Turpin also said that the dog might not be what made the difference: "It could potentially be because dog owners get outside more often with their pets or live in areas with more green space, which has been shown previously to protect against Crohn's." Cats showed no effect. Everyone in the study also had a close relative with Crohn's, so the result may not carry over to people without that family history.

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What your dog can pass to you

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The CDC (the US government's public health agency) doesn't say anything about dogs improving your microbiome. Its dog page says that dogs can sometimes carry germs that can make people and other animals sick, and its puppy page adds that healthy dogs can carry Campylobacter bacteria and other germs that can make people sick, and that some strains have spread to people through contact with dogs, pet store puppies especially.

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A 2026 study from China looked for antibiotic resistance genes (genes that help bacteria survive antibiotics) in dogs and the people living with them. Dog owners carried more of certain ones in their gut than people without dogs, and the authors concluded that living with a dog is associated with a shared gut "resistome" (the full set of resistance genes your gut bacteria carry). Only the summary of that study is free to read, and it doesn't say how many people were tested.

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The CDC tells dog owners to always wash their hands thoroughly with soap and water right after touching their dog, after handling its food, and after cleaning up after it, and not to let dogs lick them around the mouth and face.

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So should you get a dog for your gut?

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If you're a teen or an adult, a dog will put its bacteria on your hands and probably do very little to your gut. Get a dog because you want one, and take care of your gut with the things that have better evidence behind them.

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