“It only takes nine kisses a day of a few seconds for the oral bacterial flora of two partners to look very similar – underlines Professor Carlo Selmi, Head of Clinical Rheumatology and Immunology at Humanitas, guest in the Tutta Salute study at Rai3.

A Dutch study by the Netherlands Organization for Applied Scientific Research in 2014, published in Microbiome, counted the bacteria that pass from one partner to another in the course of a deep kiss: 80 million and 700 different strains.


Bacteria, training for the immune system

“One of the great discoveries of recent decades is that most bacteria in our body have an active part. For each cell of our body we have about ten bacteria, between the intestine and the skin above all, and these serve as a gym for our immune system. We know today that the diversity of the bacterial population in our bodies is just as important as training for our immune system.

Patients with rheumatoid arthritis, for example, or with a disease linked to psoriasis, tend to have a less varied intestinal bacterial flora and therefore this is associated with a higher level of inflammation than those with a different flora,” said Professor Selmi.


Microbiota, it is not only intestinal

“There is an intestinal microbiota, which is the one we know best, but there is also one in the skin, so the bacteria present on the palm of our hand are different from those on the back, and there is a microbiota inside our mouth. Some of these bacteria are diseases of the oral cavity, such as caries or periodontal disease,” the specialist pointed out.


Bacteria exchange

A couple that have lived together for a long time and who share physical contact with kisses and effusions, also exchanges immune information.

“The two bacterial populations will tend to resemble each other, to level out in a similar way. The study showed that it only takes nine kisses a day of a few seconds for the oral bacterial flora of two partners to look very similar,” said Professor Selmi.

If, therefore, the kiss has always belonged to our social behavior, this gesture could contain some evolutionary secrets, which could have an explanation in the exchange of bacteria.


Watch the full interview with Professor Carlo Selmi from minute 37.26, click here.