But that's actually a good thing, researchers say.
WEDNESDAY, July 26, 2017 (HealthDay News) -- While it's often said that couples start to look alike over time, new research suggests their skin bacteria may do the same.
The study, of 20 couples who were living together, found that partners showed similarities in their skin's "microbiome."
In fact, those similarities were strong enough that a computer algorithm could identify couples 86 percent of the time, based on their skin microbiome alone.
"Microbiome" refers to the trillions of bacteria and other microbes that inhabit the human body, inside and out. The skin is covered in a variety of microbes --- most of which are either harmless or beneficial.
Researchers are only beginning to understand how the skin microbiome affects health, according to study senior researcher Josh Neufeld, a professor of biology at the University of Waterloo in Canada.
But the "microbial community" there does interact with the immune system, and it might have a bigger health impact than traditionally believed, explained Neufeld.
So, he said, it's important to understand what factors affect the makeup of any one person's microbiome.
The new findings point to the importance of the home.
Although the study focused on couples, Neufeld explained, it seemed that contact with the same home surfaces -- rather than contact with each other -- was key.
Couples showed the greatest microbial similarities on their feet -- which makes sense, Neufeld said.
"You shower and walk around barefoot in the bathroom, spreading your microbes around," he said.
But Neufeld was also quick to point out that none of this is "gross."
Diversity in a person's microbiome -- whether in the gut or on the skin -- is healthy, he said: Good bacteria keep the bad guys in check.
A lack of diversity in the gut's microbial community has been linked to increased risks of certain conditions related to metabolism and immune function -- including obesity, type 1 diabetes and asthma.
There has been less research into the skin's microbiome, said Dr. Adam Friedman, an associate professor of dermatology at George Washington University in Washington, D.C.
But there's evidence that a lack of diversity in skin microbes might contribute to eczema, acne and rosacea, said Friedman.
The fact that couples share skin microbes isn't surprising, Friedman said.
But, he added, "this [study] highlights the importance of the external environment on our skin's microbial community."
Friedman echoed the point that "diversity is good."
"We usually talk about bacteria like they're bad," he said. "But when everything is in harmony, there is no 'good' or 'bad.' When there's a lack of diversity, and that harmony is thrown off, we have a problem."
In the new study, published recently in the journal mSystems, the Canadian researchers analyzed skin swabs that each participant collected from 17 different sites on the body.
In general, the study found, couples had similarities in their skin bacteria -- enough that they could usually be identified as partners.
"But," Neufeld said, "it's not that you look just like your partner. You look like you."
And much depended on the specific area of skin: Bacteria on couples' feet showed the most similarities; the bacteria on their inner thighs looked nothing alike.
Instead, women looked more like other women when it came to bacteria there. According to Neufeld, that is probably a reflection of vaginal microbes.
Biological sex is a big factor in the makeup of skin bacteria, Neufeld said: Women seem to have more microbial diversity than men -- which may, in part, be due to differences in the skin's acidity.
"Our bodies, and the chemicals they secrete, help determine which bacteria survive and thrive," Neufeld said.
Many other factors also sway the skin's microbial balance, Friedman said. They include factors we cannot change -- age and genetics -- and some we can control -- from sun exposure to soaps and skin products.
It's not clear whether having your family's microbes on your skin makes any specific difference in your health. But Neufeld said there's no reason to fear sharing some microbes at home.
"If you're in an airport, sure, don't walk around barefoot," he said. "But at home, go ahead and do it."
The U.S. National Institutes of Health has more on the human microbiome.