While you'd never lick a stranger, chances are you get all up in your partner's mouth when you kiss. Ever wonder if that's remotely sanitary?
Recently a team of researchers set out to measure how much bacteria you transfer when you kiss. In a new small study recently published in the journal Microbiome, they asked 21 couples about kissing frequency and gave one person in each duo a probiotic beverage to drink before planting a passionate kiss. To really kill the romance, researchers took saliva samples to measure bacteria before and after the kiss. On average, one 10-second kiss transferred about 80 million bacteria to people who didn't drink the beverage.
While this might sound supremely gross, saliva contains approximately 1 billion microbes, so 80 million isn't that many. And transferring bacteria isn't always such a bad thing, says study author Remco Kort, a microbial genomics professor at Netherlands Organization for Applied Scientific Research. Kissing temporarily increases the diversity of bacteria in your mouth and on your tongue. Because mouth bacteria have protective qualities, literally swapping spit could potentially enhance your immune system to make you more resilient, Kort says. The bacteria in your mouth may even prevent the bad bacteria from colonizing when you kiss someone who's sick.
For what it's worth, the researchers also found that couples had more similar saliva bacteria than strangers regardless of how often the couple kisses. While the kissing itself does appear to play a role, other commonalities—like using the same toothpaste or sharing meals—could contribute too. Which is something to remind your partner when you want to share his cheeseburger (and kiss him afterward).
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.