A kiss is just a kiss—except for when it's a major bacteria conduit. A new study published in Microbiome takes a look at what happens when we kiss intimately, and finds that 10 seconds of passion can result in the transfer of up to 80 million bacteria. Dutch researchers examined 21 couples who outlined their kissing behavior via a questionnaire; the participants were then swabbed and analyzed, and the researchers found that couples who reported sharing no less than nine intimate kisses daily (meaning there was both full tongue contact and saliva exchange) had a "shared salivary microbiota." Then came the experiment designed to quantify the bacteria flow: One half of each of the couples drank a probiotic yogurt drink containing known varieties of bacteria that aren't typically found in the mouth, notes Time.
An intimate 10-second kiss followed, and the researchers then analyzed the effect of the receiver's saliva: the amount of probiotic bacteria jumped threefold, a press release explains, and the researchers crunched the data and came up with the 80 million figure. As one researcher puts it, "kissing is very healthy," in that the more bacteria we're exposed to, the stronger our resistance can potentially become. A fascinating side note: Most couples reported very different kissing tallies, with 74% of men reporting more smooches than their female partners did, at an average of 10 French kisses a day, compared to women's five. And in one case, a man reported an average of 50 intimate kisses a day, to his partner's eight; as such, their numbers were excluded from some of the calculations. (Another study dug into why kissing matters.)