Compatibility and The Gut Microbiome

• Compatibility in relationships isn't just about personality or shared interests—it also involves biology through the gut microbiota.

• Romantic relationships can influence microbiota diversity through shared environments, behaviors, and physical interactions.

• Microbial transfer from activities like kissing and touch plays a key role in shaping the microbiota of both partners.

Higher relationship satisfaction and intimacy are linked to greater gut microbial alpha diversity, the richness of the bacteria in your microbiome (Le Chatelier et al., 2013). This should not be a surprise as couples will have a more diversified diet than an individual would. This increase in diversity has its benefits to your health.  Alpha diversity, which reflects a more varied gut microbiota, has been associated with a reduced risk of chronic diseases. Additionally, less holding back in relationships were found to correspond with higher gut microbial diversity. These findings imply that positive relationship dynamics correlate with a more diverse and balanced gut microbiome, potentially supporting better overall health. Married individuals, especially those in close relationships, have a more diverse and richer gut microbiota compared to those living alone. Couples with somewhat close relationships, however, did not differ significantly from unrelated individuals, showing that the strength of the relationship plays a key role in determining similarity of the gut (Chang et al., 2023). The strength of the relationship has a more substantial impact on gut microbiome composition than shared genetics or early life environments in siblings (Dill-McFarland et al., 2019). While the role of shared diet wasn't definitive, physical intimacy could be a key factor, with its influence evolving throughout life. Stronger relationships may do more than boost emotional well-being, they could also support a more diverse gut microbiome.

A study examined the impact of kissing on the salivary and tongue microbiota of 21 couples, revealing that kissing partners tend to have more similar oral microbiota compared to unrelated individuals, with the most pronounced similarity on the tongue's surface. The researchers found there was a clear correlation between the frequency of kissing and the similarity of salivary microbiota. They also quantified bacterial transfer during kissing, with an average of 80 million bacteria exchanged during a 10-second kiss, primarily from the Lactobacillus and Bifidobacterium species. The tongue microbiota’s similarity between partners appears less influenced by kissing behavior and more by shared lifestyle factors, such as diet and environment, along with possible genetic influences (Kort et al., 2014).

Even the skin microbiome can be influenced by many factors and cohabitation is one of them. A study examined the skin microbiomes of 20 people from 10 cohabiting couples, sampling from 17 different areas of the body. The research found that living together significantly shaped their skin microbiota, with the closest similarity between partners found on their feet. Daily interactions and shared environments, like cohabitation, can impact the composition of our microbiomes and potentially affect our health (Ross et al., 2017).

People in close relationships tend to share more microbial strains, with frequent meals and time spent together increasing this exchange. This sharing extends beyond direct relationships, influencing even friends-of-friends. Over time, socially connected individuals continue to develop more similar microbiomes, while socially isolated people have less microbial diversity (Beghini et al., 2025), these instances are referred to as “cohabitation similarities”. Those with a central role in their community also have more representative microbiomes, highlighting how social networks create pathways for microbial exchange and support a better gut ecosystem.

We’ve discussed before the gut-brain axis and the bidirectional power it holds over us, so it's not surprising that it plays a significant role here in a discussion of love and the gut. You may have heard people talk about “love chemicals”, (Harvard Medical School, n.d.) and their release during physical affection or even seeing your favorite person. These love chemicals are generally our “feel good” neurotransmitters, including dopamine, and oxytocin. 

The gut microbiota is essential for dopamine metabolism, with its enzymatic activity facilitating both dopamine synthesis and the breakdown of dopamine's subsequent metabolites. Key genera, including Prevotella, Bacteroides, Lactobacillus, directly influence dopamine levels (Hamamah et al., 2022).

While microbial communities are initially shaped by transmission from mother to child, social interactions later in life further affect their composition and diversity. Those people with larger or more diverse social networks tend to have more diverse microbiomes. The structure of social networks therefore acts as a conduit for the exchange of beneficial microbial strains, making strong, frequent social connections vital not only for social wellbeing but also for microbial diversity and overall gut health .

While science has yet to fully explain the underlying reasons for attraction, it remains a phenomenon as ancient as living, reproducing organisms. The similarities between your gut microbiome and other persons can indicate that you've likely been exposed to similar environments, stressors, stimuli, and even comparable diets. For couples, getting their microbiomes tested together could offer fascinating insights into their shared microbial makeup, potentially revealing deeper biological connections and even sparking discussions about health, diet, and lifestyle compatibility.