Turns out kissing really can give you cooties.

A new study says that an intimate 10-second kiss can transfer up to 80 million bacteria. The study was published in the journal Microbiome and tested saliva from 21 couples. These couples, ages 17 to 45, were passionately kissing, not just exchanging short pecks, study authors said.

“Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behavior unique to humans and is common in over 90 percent of known cultures,” Remco Kort, microbiologist and lead study author, said in a statement.

People who also kiss at least nine times a day are more likely to have the same saliva microbes in their mouth.

“To our surprise, we found that those people that are intimately related ... share much more of that bacteria on their tongue than unrelated individuals," Kort told NPR.

Should you be worried about swapping bacteria back and forth? Not so much, Dr. Wenyuan Shi, a professor of microbiology at the University of California, Los Angeles, told Today.com. Unless you have cavities, the bacteria can't really affect you, he said.

The thought of 80 million foreign bacteria in your mouth may be gross, but here's a pretty good reason to keep smooching: kissing can lower your stress levels.