Kissing is one of the most common sexual and romantic behaviors in America and many other parts of the world. But have you ever stopped to wonder why? Why did humans ever start kissing in the first place? Is it just because it feels good, or is there something more to it than that?

Scientists increasingly believe that kissing is an adaptive behavior. Not only does it help us to identify good partners, they argue, but it might also be beneficial for our health and relationship happiness.

INFORMATIONAL KISSING
First, kissing appears to help us “size up” potential partners. As evidence for this idea, researchers have found that women and people who are very attractive place the most importance on kissing. In other words, people who tend to be “choosier” about their mates and hold them to higher standards are more likely to evaluate their partners based on the way they kiss.

These folks are also the most likely to say that their attraction to someone else has changed based on a first kiss.

Other research has found that when women are at the most fertile stage of their menstrual cycle, they think kissing is even more important. Thus, when women have the greatest odds of becoming pregnant, they’re most likely to use kissing as a mate-assessment tool.

JUST LIKE TINDER ONLY FUN
So how exactly does kissing help us determine the quality of potential partner? That’s not entirely clear yet, but scientists speculate that it’s because kissing allows us to quite literally smell and taste another person.

Specifically, when we get up close and personal with our noses and mouths, we can detect pheromones and other chemical signals that may help us to subconsciously determine whether a partner is healthy, fertile and carrying good genes.

We may use kissing to determine who is good mating material and who isn’t.

WHAT ABOUT KISS NUMBER 1,000?
Of course, we don’t just kiss when we’re looking for a partner—people in long-term, monogamous relationships continue to kiss each other, despite having already sized each other up.

This kind of kissing is thought to serve a few different purposes.

Kissing can be good for a relationship because it’s a way of expressing affection and developing intimacy. Consistent with this idea, some studies have found that frequent kissing—but not frequent sex—is linked to greater relationship satisfaction.

Regular kissing may also help us to maintain good health by promoting the exchange of certain microorganisms.

A 2014 study found that kissing promotes the exchange of a ton of bacteria. In fact, as many as 80 million bacteria may be exchanged in a single deep kiss.

This study also found that the more frequently couples kissed, the more similar the bacterial colonies in their mouths were.

So how might this extensive transfer of microorganisms affect our health? One possibility is that kissing may be a way for women to protect their offspring from certain infections.

For example, some researchers argue that kissing might allow women to contract infections like human cytomegalovirus (HCMV) prior to becoming pregnant—a time when this infection is unlikely to cause any problems. When women contract HCMV during pregnancy, though, it can be harmful to the developing fetus.

Kissing may therefore be a way that women can control the timing of their exposure to this and other infections such that it benefits the health of their children.

AND SO…
The science of kissing suggests that lip-locking is probably more important than you ever realized. Not only can being a good kisser help to boost your sex appeal, but kissing early and often just might make you happier and healthier in the long run.