Romantic kissing happens in over 90 percent of all cultures, and with good reason: “It helps us find a partner and stay with them,” says Laura Berman, PhD, assistant clinical professor of ob-gyn and psychiatry at the Feinberg School of Medicine at Northwestern University in Chicago and author of Loving Sex ($25, amazon.com). But it also has a slew of surprising functions, including some major health benefits. Pucker up to these fascinating facts.

It may be the most fun way to build immunity
Just 10 seconds of French kissing can transfer 80 million germs from one person’s mouth to the other, according to a Dutch study published this past November in the journal Microbiome. While that may sound gross, there’s a big potential benefit.

“It’s a way to pass around bugs so your body develops immunity to them,” Berman explained.

In fact, a 2010 paper in the journal Medical Hypotheses suggested that kissing between partners could help protect their babies from being infected in utero with cytomegalovirus, which can cause birth defects such as infant blindness.

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It really is ‘in his kiss’
Women rate romantic kissing as more important when they’re close to ovulation—in other words, when they’re more likely to get pregnant. This makes sense from an evolutionary perspective, researchers say: Kissing offers a way to assess a mate through taste or smell.

It may boost your libido
While both sexes enjoy French kissing with long-term partners, guys “preferred more tongue contact” than women with short-term mates, according to a study published in the journal Evolutionary Psychology in 2007. (The study was done with college students, so you might want to take it with a grain of salt.)

“One theory is that their saliva transfers testosterone to the woman, which in turn increases her sexual desire,” explained Berman.

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It boosts happy hormones
“When you kiss, your brain releases this chemical that leaves you feeling connected and bonded to your mate,” explained Berman.

It also releases endorphins, those same feel-good chemicals your body produces when you work out. Another relaxing bonus: kissing lowers levels of the stress hormone cortisol, according to a 2009 study done at Lafayette College in Pennsylvania.

It may save your relationship
Both men and women who report frequent kissing in their relationship report more sexual satisfaction, according to a 2011 Kinsey Institute study. Guys who frequently smooched were also three times happier in their relationship than guys with limited snuggling. (Interestingly, frequent kissing didn’t predict relationship satisfaction for women.)

It can last for days—literally
The longest kiss award goes to Ekkachai Tiranarat and Laksana Tiranarat, who smooched for 58 hours, 35 minutes and 58 seconds in Pattaya, Thailand, on February 12-14, 2013. They beat out eight other couples who entered the competition. Wonder how much training they had to do to prepare for that one!

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This article originally appeared on Health.com.