80 million bacteria transferred in a kiss

Warm fuzzy feelings are not the only things being shared when you kiss someone — a study published in science journal Microbiome reveals that a single, 10-second kiss can transfer as many as 80 million bacteria. The study also discovered that couples who kiss each other more than nine times a day share similar communities of oral bacteria.

The microbiome, which is the huge ecosystem of more than 100 trillion microorganisms that live in our bodies, is essential for keeping us healthy. The mouth alone hosts more than 700 varieties of bacteria.

The two-part study was performed by a team of researchers from the Netherlands Organisation of Applied Scientific Research. In the first part, they asked 21 couples to fill out questionnaires for their kissing behavior, such as how frequently they kissed each other in the past year and when they had last kissed. After the questionnaire, the researchers collected samples of each individual’s oral bacteria by swabbing their tongues and collecting saliva. As it turns out, couples who reported that they kiss very frequently had more similar communities of bacteria in their saliva compared to those who rarely shared a peck.

For the second, controlled part of the experiment, one member of each couple drank a probiotic drink that contained specific types of bacteria including Lactobacillus and Bifidobacteria. After a 10-second kiss, the researchers found that the quantity of probiotic bacteria in the receiver’s saliva rose threefold. The calculations, which are based on average transfer values and a number of assumptions related to bacterial transfer, the kiss contact surface and the value for average saliva volume, come out to a total of 80 million bacteria that were transferred with the kiss.

Researchers believe that the similarity in oral bacteria amongst couples could also be due to other variables, such as similar lifestyles, diets and personal care habits.

But before you start regretting last weekend’s hookup, researchers think this could actually be a very good thing — the bacteria that were transferred do not do much harm and could even help deter pathogenic bacteria from moving in by just taking up space. Other scientists suggest that French kissing could help shape the immune system. Kissing provides access to a huge number of microorganisms, and exposure to someone else’s non-pathogenic bacteria could help build up immunity.