Poets consider him the pink apostrophe among the words “I love you”. Doctors consider it a nostrum for the immune system. Whatever the perspective, the kiss represents a source of well being: mental and physical. According to Professor Carlo Selmi, Head of Clinical Rheumatology and Immunology at Humanitas, “it takes just nine kisses a day of a few seconds for the oral bacterial flora of two partners to look very similar”. A Dutch study by the Netherlands Organization for Applied Scientific Research in 2014, published in Microbiome, revealed that 80 million different strains of bacteria pass from partner to partner in a deep kiss.
Training for the immune system
Bacteria can be a source of disease, but they can also be a source of wellbeing. For each cell of our body we have about ten bacteria, between the intestine and the skin above all, and these act as a real gymnasium for our immune system. “Patients with rheumatoid arthritis or with a disease related to psoriasis – Prof. Selmi – tend to have a less varied intestinal bacterial flora and this is associated with a higher level of inflammation than those with a different flora. In short, it seems that the microbiota, known to be in the intestine, is actually spread everywhere a little. There is also one in the skin, so the bacteria 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 also responsible for oral diseases, such as caries or periodontal disease.
All it takes is 9 kisses a day
A kissing couple sharing physical contact also exchanges immune information. “The two bacterial populations will tend to resemble each other, to level out in a similar way – added Selmi. 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”.