From the Department of Things You’d Think Would Be Obvious, some Dutch scientists have determined that “intimate kissing” (that’s apparently the technical scientific term for “French kissing”) transfers bacteria between the mouths of the participants, and also, if they look at the bacteria in your mouth and the bacteria in the mouth of someone you make out with on a regular basis, they’ll find a lot more similarities than, say, if they check the mouth of your next-door neighbor.
To figure this out, they recruited 21 couples visiting a zoo. Everyone filled out a questionnaire on how frequently they kiss. Hilariously, the men very consistently gave higher estimates on how often they kissed than the women did, in one case to the point that they tossed the data: “One report of an average of 50 intimate kisses per day over the last year was according to the opinion of the authors unrealistically high, not in agreement with the reported time to latest kiss of 18 h and showed a large discrepancy with the self-reported kiss frequency of his partner of eight intimate kisses per day.” The study included one lesbian and one gay male couple; I couldn’t find any reports on whether they produced more closely-matched kiss estimates. Everyone’s tongue got swabbed, and they spit into a vial. They also had one person drink a probiotic yogurt drink; the couple was then asked to kiss for at least ten seconds, and then their tongues were swabbed again. That’s how they got the number that all the newspaper articles are quoting: that you transfer 80 million bacteria every time you share an intimate kiss at least ten seconds in duration.
The NPR reporter called up a few scientists who were not involved in the study, and quoted a microbiologist from the University of North Carolina suggesting that perhaps we could transfer saliva from the mouth of someone who gets very few cavities into the mouth of someone with serious tooth decay issues. There have actually been significant studies in the past on microbiota and tooth decay: to sum up, you get tooth decay because of S. mutans, and you almost certainly got it from your mom. Anyway, other microbes that might have protective factors is an interesting idea.
Anyway. Even though nothing in the kissing study should be remotely surprising (other than their ability to pull a specific figure out of the data), it’s been reported all over for the simple reason that it’s kind of the ultimate straight line for jokes about the fact that with the right kind of scientific data, you can make kissing sound every bit as gross as you thought it was back when you were nine.
My favorite thing about this study (well, aside from the fact that on average, the men estimated exactly twice the amount of kissing that the women did) is the image of these scientists recruiting a bunch of people to make out for science while they were on a date to the zoo. In addition to proving that you pass bacteria around when you make out, I’d say they also proved that Dutch people are extremely good sports.