Those who think that love is the only thing exchanged with a kiss should think again. The “seal” of the poets is a powerful “vector” for the transmission of bacteria.

To reveal what happens during the outpouring of the most romantic and passionate effusion, a dutch research group counted the bacteria jumping from tongue to tongue: 80 million bacteria and 700 different strains. All the microorganisms that were counted are included in the study of the Netherlands Organisation for Applied Scientific Research published on Microbiome.

No worries though, the kiss remains a gift that is generally harmless. “In fact – says Professor Carlo Selmi, immunologist and Head of Rheumatology and Clinical Immunology at Humanitas – if the kiss is part of our set of social behavior from the beginning of time, surely there must be some secret in this evolutionary gesture. There might be an explanation for the exchange of bacteria”.

However, it is an explanation that science is not yet able to provide. “Yet another fact seems to confirm the importance of the kiss”, the specialist continued. It is “the fact that 90% of living species have exchanged kisses and bacteria in addition to the alterations of intestinal flora and the skin that characterize inflammatory diseases of the skin and intestines”.

We are made of bacteria

The experiment was conducted in two phases. In the second the 21 participating couples was distributed a probiotic. This allowed a more reliable count after 10 seconds of kissing, especially to ascertain the identity of the oral bacterial species after the kiss. As if it were a process of biological approval, in which the bacteria play a fundamental role.

“Just think – continues Dr. Selmi – that each of us has more bacteria than cells, and there are crowded colonies in flux, especially those that are the gateways to the outside: the mouth and gastrointestinal tract in particular.”


The non-scientific idea of not thinking of bacteria as something dangerous should, therefore, be amended. “Fortunately, scientific research is increasingly putting out the complex and it is yet to decipher the difference between the bacteria that live in us and diseases, showing that imbalances can be harmful and notable for the emergence of autoimmune diseases, but especially that excessive hygiene is a factor that exposes the body, referring to the skin, to damage rather than greater security.”