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By Meghan Holohan, NBC News contributor

If you’re a dog person, you may have more in common with your fellow dog owners than you even realize. 

New research shows that two strangers who both own dogs are more likely to share similar skin bacteria than a married couple without a dog in the home. The study also found that dogs have more skin bugs in common with their human owner than other dogs.

Researchers examined the skin of people who lived together – couples, couples with dogs, couples with children and couples with children and dogs – and found that the family dog very generously shares his skin bugs with his owners. The groups with dogs in the home shared more skin bacteria than any of the other cohabitating groups studied. Not surprisingly, doggy affection is behind all this sharing – dogs transmit their skin microbes to their people via tongue-to-skin, skin-to-skin or paw-to-skin contact.

If you’re not a dog person, you might find all of this a little gross. But remember, our skin is already teeming with thousands of kinds of bacteria, and those microbial colonies help keep us healthy by bolstering our immune systems or aiding digestion, for example. Plus, the researchers assure that picking up some doggy bacteria is not harmful to humans.

“Most of the dogs’ [microbes] will be more beneficial than harmful,” says Rob Knight, a co-author of the new report and an associate professor at the University of Colorado, Boulder. He points out that past studies have shown that kids who grow up with a dog in the home have lower rates of asthma and allergies.

Knight and his colleagues wanted to find out how cohabitating couples spread microbes, and if they contributed to each other’s microbiome – that’s the entire collection of microorganisms living in an environment (in this case, our bodies). They took oral, skin, and fecal samples from 159 people: 17 families with cohabitating children from six months to 18 years old; 17 families with one or more dogs but no children; eight families with both children and canines; and 18 families with no dogs or kids. The researchers also took samples oral, skin, and fecal samples from the dogs. They then analyzed all the samples to see how much overlap existed.  

He suspected that couples with young children would have the most microbes in common; kids seem like a hotbed of microbes and caring for them means couples face the same exposure. But that’s not the case – families with canine family members shared more microbes. Interestingly, the same isn't true for cat owners, possibly because our feline friends are less social. (Besides, everyone knows cats hate sharing.) When Spot bestows a lick of love, he’s also giving a gift of betaproteobacteria, and when he offers a paw shake it comes with a side of actinobacteria. These two doggy microbes were most often found on their owners’ skin.    

Even though the dog-human microbial bond is strong, Knight notes that families show evidence of having similar microbiomes. Even still, each person’s microbial makeup is singular. 

“It is fascinating how different and unique that the microbial communities on people are,” he says.

While it might make our skin crawl to consider that we have something like 100 trillion microbes in and on our bodies compared to our 10 trillion cells, Knight assures us that microbes are friendly.

“Microbes are actually helpful,” he says. “If most of the microbes were out to get us, we’d really be in trouble.”

The study appears at the online journal eLife. And if you're interested in participating in research mapping human microbes, sign up here.

Related: 

• Roller derby skaters trade bumps, bruises and bacteria

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Members of the Detroit Derby Girls Travel Team battle The Chicago Outfit Syndicate during a women's flat track roller derby bout in Detroit, Michigan, in April 2011.

The women of roller derby are always crashing and smashing into each other, constantly trading bumps and bruises -- and at the same time, they're also trading the microscopic bugs living on their skin. That's according to a new study that used derby to investigate the way contact sports can mix up our skin microbiome. 

"As a derby skater, I was always curious about the unseen ways my teammates influenced me," says Jessica Green, the director of the University of Oregon's Biology and the Built Environment Center, who co-authored the new paper, published online today in the new journal PeerJ. Green is also a former jammer - that's the skater who scores the points - with the Emerald City Roller Girls of Eugene, Ore. (Her derby name: "Thumper Biscuit," she says.) 

"When I was on the track learning a new move - like 'jumping the apex' - my mind would drift to science and 'microbiome land,'" Green says. "I realized that contact sports are an ideal venue to explore if and how touching mediates the exchange of microbes among people in a group setting." 

We know, even if we don't always like to remember it, that our skin is teeming with thousands of kinds of bacteria, and we also know that those microbial communities protect us from pathogens and help regulate our immune systems. But Green and her fellow researchers at the University of Oregon wanted to know more about where we get those microbes, and how those invisible bacterial communities are changed and distributed every time we touch each other.

"For years, most of what we knew about the skin microbiome came from medical studies targeting important pathogens dispersed between sick people and health care staff in a hospital setting," explains lead author James Meadow, a postdoctoral research associate at the University of Oregon's Biology and the Built Environment Center. "This study enabled us to look at whole communities of microbes being passed between healthy people." 

And roller derby -- where players jockey for track position by bumping upper arms, hips or, ah, "booty" (seriously, that's the official roller derby nomenclature) -- seemed like an ideal contact sport to study to find out.

"Over the years I've noticed it's hard to get folks interested in microbes. Maybe it's because you can't see microbes with the naked eye and they are also are misunderstood as being gross," says Green, whose derby past helped with planning the logistics for co-author Keith Herkert, who did the project for his undergraduate honor's project. "Adding roller derby into the mix makes microbes a lot more appealing."

Women from the Emerald City Roller Girls of Eugene, Ore.; the D.C. Roller Girls of Washington, D.C.; and the Silicon Valley Roller Girls of San Jose, Calif., participated in the study, and all skin samples were collected at the Big O Tournament in Eugene on Feb. 10, 2012. All the women were swabbed in the same small area of their upper arm, one area of the skin that is exposed and frequently bumped during a match, or "bout."

After a DNA analysis, the researchers found that teams had similar, distinct microbial communities. "For example, if we had picked a player out at random before they skated in the tournament, I probably could have told you what team she played on," Meadow says. The samples for the D.C. team, for example, contained Brevibacterim, and the samples from the Oregon skaters were similar to the surface samples taken from their home track. But after the teams competed, the hour-long bout mixed up their microbes, leaving opposing teams with more similar-looking microbial communities, the analysis found. Specifically, six different kinds of bacteria - Strepococcus, Sphingomonas, Eubacterium, Porphyromonas, Aerococcus and Methylobacterium - were shared by competing teams after, but not before, the bout.

Next, Meadow and his fellow researchers want to understand how long those similarities last, and how sharing our microbes influences our health in the long term. 

As Green explains it, using roller derby is an easier-to-follow example of how we literally influence each other on a microbial level.  "The people we choose to be in community with -- through sports, work, and social circles -- likely influence our personal biome in ways we never imagined," Green says. 

"Our bodies are home to countless microbes that help define who we are," she continues. "Our health and well-being depend on our microbes. People that have the right cocktail of microbes on their skin, for example, are better positioned to fight off germs or pathogens, because their good microbes out-compete the bad invaders. We currently know very little about where our personal microbial communities come from. Our study suggests that our microbes come, in part, from the people we touch. "

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