It depends on who we’re kissing Share on Pinterest Humans pucker up for all kinds of reasons. We kiss for love, for luck, to say hello and goodbye. There’s also the whole ‘it feels so good’ thing. And when you stop and really think about the act of kissing, it’s kind of strange, isn’t it? Pressing your lips against someone else and, in some cases, swapping saliva? It turns out there’s some science behind this strange but enjoyable behavior. There are many theories about how kissing originated and why we do it. Some scientists believe that kissing is a learned behavior, since roughly 10 percent of humans don’t kiss at all and considerably fewer kiss with romantic or sexual intent. Others believe kissing is instinctual and rooted in biology. Have a look at some of the science behind kisses of all kinds and see what you think.

Some kisses are rooted in attachment Kissing causes a chemical reaction in your brain, including a burst of the hormone oxytocin. It’s often referred to as the “love hormone,” because it stirs up feelings of affection and attachment. According to a 2013 study, oxytocin is particularly important in helping men bond with a partner and stay monogamous. Women experience a flood of oxytocin during childbirth and breastfeeding, strengthening the mother-child bond. Speaking of feeding, many believe that kissing came from the practice of kiss-feeding. Much like birds feeding worms to their little chicks, mothers used to — and some still do — feed their children their chewed up food.

Some kisses are rooted in romantic love You know that high you feel when you’re head over heels for a new love and spending time canoodling with them? That’s the effect of the dopamine in your brain’s reward pathway. Dopamine is released when you do something that feels good, like kissing and spending time with someone you’re attracted to. This and other “happy hormones” make you feel giddy and euphoric. The more you get of these hormones, the more your body wants them. For some, this may be more apparent at the start of a relationship — especially if most of your time is spent in a lip lock. If you can keep up a steady pace of kissing after that initial spark fizzles, you can continue to enjoy the benefits of those happy hormones. You may even have a more satisfying relationship. In a 2013 study, couples in long-term relationships who frequently kissed reported increased relationship satisfaction.

And some kisses are spurred by your sex drive It’s no secret that some kisses are totally sex-driven and far from platonic. Older research shows that for women, kissing is a way to size up a potential mate. It also plays an important role in their decision to hit the sheets. Female participants said they were less likely to have sex with someone without kissing first. They also reported that how well someone kisses can make or break their partner’s chances of getting to third base. It’s also been shown that men kiss to introduce sex hormones and proteins that make their female partner more sexually receptive. Open mouth and tongue kissing are especially effective in upping the level of sexual arousal, because they increase the amount of saliva produced and exchanged. The more spit you swap, the more turned on you’ll get.

Plus, kissing (of any type) just plain feels good You can thank the many nerve endings in your lips for their part in making kissing feel so very good. Your lips have more nerve endings than any other part of your body. When you press them against another set of lips or even warm skin, it just feels good. Combine that with the chemical cocktail released during kissing, and you’ve got a recipe that’s sure to give you all the feels. Along with the oxytocin and dopamine that make you feel affection and euphoria, kissing releases serotonin — another feel-good chemical. It also lowers cortisol levels so you feel more relaxed, making for a good time all around.