Our bodies consist of an ecosystem of more than 100 trillion microorganisms know as the microbiome. They are essential for digesting food, synthesizing nutrients and preventing disease. Shaped by genetics, diet and age the microbiome is also shaped by the individuals with whom we interact. Our mouths play host to more than 700 varieties of bacteria and the oral microbiota are greatly influenced by those closets to us.

The open access journal, Microbiome, has found that as many as 80 million bacteria are transferred from person to person during a simple 10-second kiss. The study found that when partners who kiss each other at least nine times a day also share similar communities of oral bacteria.

Researchers of Micropia and TNO in the Netherlands studied 21 couples. These couples were asked to fill out questionnaires based on their kissing behavior, which included their average intimate kiss frequency. Swab samples were taken of the couples in order to investigate the composition of their oral microbiota and their tongues and in their saliva.

When couples kiss intimately at high frequencies the results show that their salivary microbiota become similar. An average of at least nine intimate kisses a day led to this significant shared salivary microbiota.

“Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behavior unique to humans and is common in over 90% of known cultures. Interestingly, the current explanations for the function of intimate kissing in humans include an important role for the microbiota present in the oral cavity, although to our knowledge, the exact effects of intimate kissing on the oral microbiota have never been studied. We wanted to find out the extent to which partners share their oral microbiota, and it turns out, the more a couple kiss, the more similar they are,” says lead author on the study, Remco Kort.

Furthermore a controlled kissing experiment was conducted to quantify the results of the transfer of bacteria. This was achieved when a member of each of the couples consumed a probiotic drink that contained specific varieties of bacteria. After the intimate kiss the receivers saliva and the quantity of probiotic bacteria found had risen threefold. This led researchers to the calculation that in total 80 million bacteria would have been transferred in those 10 seconds.

From the study it also found that there were important roles for other mechanisms that select oral microbiota, which is the result of a shared lifestyle, dietary and personal care habits, especially on the tongue. Microbiota on the tongue were much more similar among partners that people who are unrelated. This similarity was found to not change with more frequent kissing however.

One last finding from the study and the questionnaires filled by couples found an interesting statistic. 74% of men from the study reported higher intimate kiss frequencies than their women partners. On average guys reported ten kisses per day where females only reported five.

Make that first kiss count. Here are 5 Tips For The Perfect First Kiss.