Exchanging bacteria in an intimate moment is a well-known fact, but perhaps not the numbers involved. A new study has found that as many as 80 million bacteria are transferred during a 10- second kiss.
The research published in the open access journal Microbiome found that partners who kiss each other at least nine times a day share similar communities of oral bacteria.
Bacteria have often been called the original natives of the planet. Ubiquitous as they are, bacteria have become essential for most living things including humans in essential tasks like digestion, nutrient synthesis and yes, even prevention of disease.
The mouth alone plays host to more than 700 varieties of bacteria.
Researchers from Micropia and TNO in the Netherlands probed 21 couples on their kissing behaviour including their average intimate kiss frequency. They also took swab samples to study bacteria population inside the mouth.
Familiarity, it turns out, breeds bacteria, not contempt.
Couples who intimately kiss at relatively high frequencies share salivary microbiota. On average it was found that at least nine intimate kisses per day led to couples having significantly shared salivary microbiota.
To study the transfer of bacteria, a member of each of the couples had a probiotic drink containing specific types of bacteria including Lactobacillus and Bifidobacteria.
After an intimate kiss, the researchers found that the quantity of probiotic bacteria in the receiver's saliva rose threefold, and calculated that in all 80 million bacteria would have been transferred during a 10-second kiss.
A shared lifestyle based on dietary and personal care habits also plays a role in shared microbiota.
Lead author Remco Kort, from TNO's Microbiology and Systems Biology department and adviser to the Micropia museum of microbes, said: "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."
The researchers found that while tongue microbiota were more similar among partners than unrelated individuals, their similarity did not change with more frequent kissing unlike the case with saliva microbiota.
The survey also stumbled upon what could throw light on the psychological side of the kiss. Around 74% of the men reported higher intimate kiss frequencies than the women of the same couple. On average ten kisses per day from the males seemed to be equal to reported five per day from the females.