Couples end up sharing the same bacteria

While it's often said that couples start to look alike over time, new research suggests their skin bacteria may do the same.

A study of 20 couples who were living together, found that partners showed similarities in their skin's "microbiome".

In the new study, published recently in the journal mSystems, the Canadian researchers analysed skin swabs that each participant collected from 17 different sites on the body.

These similarities were strong enough that a computer algorithm could identify couples 86% of the time, based on their skin microbiome alone.

An icky situation

Some microscopic organisms called bacteria can cause diseases in humans. When this occurs, it is called a bacterial infection.

There are thousands of different types of bacteria all over the world. Only a few types of bacteria cause disease in humans.

"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 these can be 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.

bacteria on skin

                               The bacteria on your and your spouse's skins may be nearly identical.

What doesn't kill you makes you stronger

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.

cleaning bathroom for hygiene

                         Your hygiene habits at home might be rubbing off on each other – literally.

Bacteria not always gross

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. "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."

Skin bacteria mostly similar

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 be partly to differences in the skin's acidity. Many other factors also sway the skin's microbial balance, Friedman said. They include factors we cannot change, such as age and genetics. Other aspects we can control, such as sun exposure and skin. 

So, if you are a bit of a germophobe and your partner is not, you might want to reach a compromise if you don't want to share the same bacteria.

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