Every time you share a long kiss with your partner, you transfer 80 million bacteria to his or her mouth. That’s the somewhat icky conclusion of a new study of 21 intimate couples at a zoo in Amsterdam. When scientists swabbed the mouths of the participants before and after they locked lips, they didn’t detect a huge change in the bacterial composition—or microbiota—of their mouths. That could be because the couples had already kissed so many times, they had become home to the same bacterial populations. It could also be that people who fall in love have similar lifestyles and similar diets, which can influence the mouth’s microbiota. To estimate just how many bacteria are transferred during make-out sessions, the team asked the volunteers for one more kiss, right after one of the partners had been drinking a probiotic yogurt, which is filled with bacteria not commonly found in the mouth. The test revealed that people transfer about 80 million bacteria to each other during a kiss, as the team reports today in Microbiome. That may sound like a lot, but the mouth is home to about a billion bacteria. So perhaps it’s not so icky after all.