Mar 30, 2026 12:00:00

Couples living together share approximately 30% of their gut bacteria. What are the health implications of sharing bacteria with your partner?

When you live with a partner, you not only share your home, lifestyle, and hobbies, but you also share the 'microorganisms' that live on and inside each other's bodies.

Conor Meehan , associate professor of bioscience at Nottingham Trent University in the UK, and his colleagues have explained the effects of sharing microorganisms with your partner.

Couples share 30% of their gut bacteria. Here's how that may affect health
https://theconversation.com/couples-share-30-of-their-gut-bacteria-heres-how-that-may-affect-health-276342

The microorganisms that inhabit the human body, consisting of bacteria, fungi, and viruses, are called the microbiome , or, including their genetic information, the microbial community, and play a crucial role in maintaining health. The microbial community of a fetus and immediately after birth is primarily formed by the mother, and as the child grows, social interactions with family, friends, and the community continue to influence the microbial community. Meehan et al. explained how much of the microbial community a cohabiting partner shares and the impact on health.

◆Intestinal bacterial flora
While diet and lifestyle are generally considered to have the greatest impact on gut microbiota, studies on couples have shown that 'living together' has a strong influence on gut microbiota. It has been reported that couples living together share 13% to 30% of their gut bacteria, and this holds true even after excluding the effect of couples eating the same diet.

Furthermore, studies have shown that couples living together have greater diversity in their gut bacteria compared to people living alone. Since gut bacterial diversity is associated with a lower risk of irritable bowel syndrome , cardiovascular disease , and hyperglycemia , Meehan et al. state that this finding is good news for couples living together.

However, depending on the type of microorganisms shared between couples, there is a possibility of adverse health effects. For example, while some species of bacteria in the Ruminococcus genus are beneficial to health, some species may increase the risk of conditions such as diabetes and irritable bowel syndrome .

◆ Oral bacterial flora
Considering that saliva is exchanged when kissing, it may not be surprising that couples share their oral microbiota.

Some studies have reported that up to 80 million bacteria can be exchanged in a kiss lasting about 10 seconds, meaning that the more a couple kisses, the more bacteria they share.

Most of the bacteria exchanged through kissing move to the intestines when saliva is swallowed, but couples are known to share a large amount of the microorganisms on their tongues that form the basis of their oral microbiome. Furthermore, it was found that couples living together share 38% of their oral microbiome, compared to only 3% for couples who do not live together.

A healthy oral microbiome is important for preventing tooth decay, has anti-inflammatory properties, and some researchers suggest it may also have health benefits for the gut and nervous system . However, Meehan et al. stated that some species of Neisseria bacteria, which are commonly found in couples living together, can cause meningitis , so further research is needed on the effects of sharing oral microbiomes.

◆Skin flora
The skin microbiome is the most unique and personalized microbiome, tailored to each individual, and is sometimes called a '

microbial fingerprint.' Studies comparing the microbiomes of family members and pets living together have revealed that skin microbiomes are more similar between couples than gut microbiomes or oral microbiomes.

For a couple's skin microbiome to match, skin-to-skin contact isn't always necessary. Everyday factors like 'sleeping in the same bed' or 'walking on the same floor' can also lead to similar skin microbiomes. This is because, just as dogs and cats shed a lot of hair, humans leave bacteria behind on everything they touch.

The impact of cohabitation on skin microbiota is significant, and a study that analyzed skin microbiota collected from various couples using computer models reported that it was possible to predict couple combinations with 86% accuracy based solely on skin microbiota. However, the impact of couples sharing skin microbiota on health is not well understood at the time of writing.

Meehan and her colleagues stated, 'While the idea of sharing bacteria with your partner might sound worrying, there's actually very little to worry about. Bacteria teach our bodies how to fight infections, help digest food, and produce essential nutrients. The bacteria you share with your partner are often harmless and, far from harming your health, can actually have a positive effect.'