So, kissing seems all fine and great, but just get science involved and, boom, we learn that it's actually pretty gross.

To be fair, our mouths are kind of disgusting to begin with: They play host to entire communities of bacteria (700 varieties!), which are part of an ecosystem of bacteria, or microbiome, that help digest and break down food. Factors including genetics and diet influence the makeup of that bacteria

But researchers in the Netherlands wondered: Hey, do couples do more than swap spit when they kiss? As it turns out, they can transfer up to 80 million bacteria. And couples who kiss often share a similar oral microbiome, according to a new study published in the journal Microbiome.

For the study, 21 couples answered questions about their kissing habits, and they also had their mouths swabbed by researchers. The couples that kissed intimately at least nine times a day — meaning they sucked a whole lot of face, "involving full tongue contact and saliva exchange," as lead author Remco Kort described it — anyway, those frequently Frenching couples "significantly shared salivary microbiota," according to the study.

Then, one member of each couple consumed a probiotic yogurt drink, followed by more making out (not exactly a recipe for romance). Researchers once again swabbed the couples' mouths and saliva to see if they transferred the yogurt's bacteria while kissing each other. The person who received the yogurt-y kiss ended up having three times the amount of probiotic bacteria after the kiss.

Researchers crunched the numbers and concluded that a 10-second kiss can transfer 80 million — 80 million — bacteria into a partner's mouth.

Kort, a microbiologist with the Netherlands Organization for Applied Scientific Research, told NPR that shared living habits, such as using the same toothpaste, may also be impacting couples' mouths. But boosting bacteria could be a good thing: "There's a number of studies that show that it's healthy to have a high diversity of microorganisms in your mouth," Kort told NPR.

As if you needed another reason to kiss.