Couples who live together agree to share a lot of things, like a bed, a bathroom, and a kitchen. Naturally, when you move in with a partner, everything changes, including your skin bacteria. Researchers at the University of Waterloo in Ontario, Canada have found when we live with a significant other, we exchange bacteria, which causes our microbial profile to change.

In the study, published in MSystems, an open-access journal of the American Society for Microbiology, researchers found each person in the relationship significantly influenced the microbial communities on their partner's skin. Using microbial data, computer algorithms were able to match couples with 86 percent accuracy. The body part most likely to host skin bacteria shared by a couple were the feet.

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Causality was not analyzed, but Canadian researchers believe it could be due to couples walking barefoot on the same surfaces in their house, therefore it's easy to transfer bacteria with each other and their immediate environment.

"You shower and walk on the same floor barefoot, and this process likely serves as an effective form of microbial exchange with your partner, and also with your home itself," said Josh Neufeld, study author and a biology professor at the University of Waterloo, in a statement.

Individuals have various skin bacterial communities from region to region, but this finding shows factors like cohabitation can actually shape one’s microbiome.

However, not all of couple's skin regions will share the same microbiome. For example, the study found microbe communities collected from the thighs were more similar between people of the same sex than those who lived together. This may be linked to the fact that bacteria on women's inner thighs are influenced by the vaginal microbiome.

Microbiomes are unique, but they can also be easily influenced. Diet, environment, and even simple chance encounters are known to affect the microbiome. It's not surprising to share a bed with someone and have their skin bacteria, since it affects the composition of your own microbial profile.

Every hour, humans shed one million biological particles via direct contact with surfaces, aerosol emissions from the body, and dust through skin cells and hair, which makes it easy to pick up new microbiomes in the environment, especially on the feet. Typically, most of the bacteria on the skin is harmless or beneficial, which prevents pathogenic microbes — bacteria that can cause infection — from inhabiting the area. The researchers believe the more we know about the risk factors that influence the human microbiome, the more we're able to understand the barriers that protect our bodies from disease. This will allow many to train their immune system and connect to the environments that people inhabit.

Microbial ecologists analyzed a total of 340 skin samples from 10 heterosexual couples currently living together to observe the influence cohabitation has on a lover’s skin. Samples were gathered via swabs from 17 sites all over the body, including the navel, armpit, and nostrils. The researchers concluded couples do play an influential role in shaping their significant other's microbial profile.

This coincides with previous research that has found married couples also influence each other's immunology. Immune systems tend to reflect lifestyle habits, like diet and exercise, which tends to coincide with couples who live together. This is why partners tend to get sick from each other, because they are in the same environment breathing in pollutants, mold and dust together.

Read More: Genetic Effect Explains Why Couples Tend To Marry Those With Similar DNA

These studies warrant further research on how microbial profiles tend to adapt and change with their host.

If you're thinking of moving in with someone, friend or partner, it's best to consider their hygiene habits and how often they get sick.

Source: Ross AA, Doxey AC, and Neufeld JD. The Skin Microbiome of Cohabiting Couples. MSystems. 2017.

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