Dutch researchers have concluded that during a 10-second French kiss, partners exchange an average of 80 million bacteria.
Their study, “Shaping the Oral Microbiota Through Intimate Kissing,” was recently published in the journal Microbiome.
The researchers conducted their investigation with the help of 21 human couples visiting Amsterdam’s Royal Artis Zoo on a summer day in 2012. They administered a questionnaire on the kissing habits of each partner in each couple and collected samples of tongue and salivary microbiota from each participant before and after a “controlled kissing experiment.” Then they offered a probiotic yogurt drink containing marker bacteria to one of the partners in each couple prior to a second French kiss to quantify the number of bacteria exchanged.
The findings suggest that a shared microbiota is able to develop in the mouths of partners. While collective bacteria in saliva were eventually washed out, those on the surface of the tongue were able to find “a true niche, allowing long-term colonization,” the researchers wrote.
“French kissing is a great example of exposure to a gigantic number of bacteria in a short time,” lead researcher Remco Kort of the Netherlands Organisation for Applied Scientific Research said in a story published online by the BBC. “But only some bacteria transferred from a kiss seemed to take hold on the tongue.