Humans are social species. Being sociable has not only allowed the human race to survive on the globe, but also to thrive for millions of years. Through social connections, the society in which we are born and live can define our personal identity, while also influencing our physiological and mental well-being.

There are trillions of microbes, fungi, viruses, and archaea in different sites of the human body that interact with their host in a symbiotic relationship. They have physiological and pathophysiological effects on the human body and psychological state. They inhabit human skin, mouth, and gut. The composition of this microbiome differs among individuals. Several factors determine the composition of the microbiome in the human body. The composition of gut microbiota is formed by diet, age, the immune system, and host genetic characteristics.

It has been shown that host genetic variations play a central role in shaping the microbiome. These genetic variations, for instance, in cells of the immune system have a central role in microbiome composition. Some studies have shown that mice with the manipulation of certain immune genes experience significant changes in their microbiome community.

People who live with us have an influence on our microbiome community.

Interestingly, people who live with us or are relatively close to us also impact the shape of our gut, skin, and oral microbiomes. This means that the people we live with, including family members, friends, and even neighbors, can have a marked influence on the composition of our microbiome. Studies have shown that family members tend to have similar microbiome communities. The microbiome has a significant impact on the functioning of body systems such as the immune system and brain cognition. Therefore, diseases associated with microbiome dysfunction, including obesity, type 2 diabetes, and cognitive disorders, could be influenced by the microbiomes of those around us.

In pregnancy, the mother's microbiome influences the gut microbiota of the baby, assisting in the digestion of food, production of metabolites, and maturation of the child's immune system. The genetic elements of the mother's microbiome form the baby's gut microbiota and produce special metabolites in the baby's digestive system. The pregnancy also alters the composition of the microbiome in mothers and subsequently affects their metabolic health. The study also showed that feeding with synthetic formula or breast milk affects the baby's microbiome.

The microbiome of couples who live together tends to have similarities, especially in terms of the microbial strains found on their skin. It has been observed that the skin microbiomes of cohabiting couples have a higher degree of microbial similarity compared to unrelated individuals. This suggests that cohabitation and sharing the same environment can influence the composition of the skin microbiome. The potential implications of these findings are the role of shared microbial communities in maintaining skin health and contributing to skin diseases.

After gut microbiota, oral cavity has the largest microbiome community, including bacteria, fungi, and viruses. Intimate kissing can influence the composition of the oral microbiota, resulting in the presence of similar microbial strains in both partners. Couples who frequently kiss each other have a higher degree of similarity in their salivary microbiota. These findings demonstrate the significance of close contact in the spread of harmful bacteria and the potential of probiotic treatment to enhance oral health.

The transmission of microbiomes between people can have serious consequences.

News about the wonderful roles of microbes in our body is spreading rapidly among academic communities and the public. If the role of the microbiome in health and diseases has not been overestimated, the findings regarding the transmission of these microbes between individuals who live in proximity have significant implications. For instance, some diseases that were not previously found communicable have now been considered to be at least partially communicable, such as diabetes or inflammatory bowel disease. Since it has been suggested that microbiota influence our decisions and desires, such as food selection behavior, a person who loves fast food may impact the food desires of their partner. Considering the role of microbes in metabolism and nutrition, it should not be far from our minds that the people around us can affect our metabolic health and even contribute to obesity.

The gut-brain axis is a hot topic of scientific research and media news. The findings of these studies suggest that the composition of these microbes influences our moods, thoughts, decisions, and behaviors. The potential transmission of the microbiome among individuals who live together proposes that similarities in microbes may result in similarities in beliefs, decision-making processes, and behaviors. This can be in addition to the thoughts and behaviors we learn directly from the people around us. Although, at present, it is an exaggeration to claim that the similarities and dependence of a couple who live together for a long time are solely the result of their similar microbiome.