Boffins have estimated that a sexy snog could transfer as many as 80 million bacteria every time a couple locks lips.
A short smooch generally feels exciting for the humans taking part, but it's even more thrilling for the tiny bugs who take the chance to embark upon an exodus into another person's body.
Some 700 types of bacteria live in the mouth, with many varieties shared by couples who regularly kiss. All they need to do is enthusiastically French for 10 seconds and 80 million mouth bugs are able to make the leap into a new orifice.
Researchers at the Netherlands [where else?] Organisation for Applied Scientific Research's Microbiology and Systems Biology (TNO) asked 21 couples about their snog schedule and then took swab samples to investigate which oral microbiota were present on their tongue and in their saliva.
An odd additional finding was that the men surveyed claimed to have been kissed more times in any given day than the long-suffering women they live with. Blokes claimed to have snogged their partner 10 times a day, whilst women said lip love only took place five times, during the same period.
Remco Kort, lead author of the paper, said: "Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behaviour unique to humans and is common in over 90 per cent 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."
The results showed that kissy couples share similar salivary microbiota. All it takes is nine (yes, nine!) french kisses a day for "significant" similarities to occur.
Happily for nervous kissers, the presence of mouth-based micro-organisms does not necessarily require an immediate visit to the GUM clinic.
Some bugs are considered "good" bacteria which chase off bad bugs as surely as many of our faces chase off potential snog partners. ®