Sex & Relationships

What Happens To Your Body When You Kiss Someone For The First Time

It’s purely chemical.

by Gigi Engle
Originally Published: 
MoMo Productions/DigitalVision/Getty Images

I’ll never forget my first kiss with my partner. It may sound cheesy, but there were fireworks. His lips were so soft, he applied the right amount of pressure, and smelled so good. I didn’t know he’d become my boyfriend at the time, but I knew I wanted him to be.

The funny thing is, up until that first kiss, I wasn’t even sure that I liked him that much. He was quiet and shy; I was loud and outgoing. But the kiss changed everything for me, which, as it turns out, is what they're meant to do.

There's a lot happening in the body during a first kiss, and "it can definitely let you know you like a person," Dr. Josh Klapow, Ph.D., a clinical psychologist, tells Bustle. "Everyone’s response is slightly different but typically we see sympathetic nervous system arousal."

This is the chain reaction that occurs when your lips lock, which your body uses as a way to assess the other person, and figure out if you're a good "match." Read on for more about what happens in the body when you kiss someone for the first time.

1. You Decide If You Want To "Mate"

While it might just seem like you're swapping spit, the act of kissing is one way the body subconsciously decides whether or not you'd want to make a baby with this person — or, at the very least, hook up.

Researchers at Oxford University looked into it and found that the chemical makeup of saliva actually lets you know if the other person would produce strong offspring. In other words, they found that kissing is designed to help you assess a potential mate.

It's also why a first kiss doesn't necessarily have to be "movie perfect" in order for it feel amazing. If you're kissing someone — and like their pheromones, which also has a lot to do with how they smell — you may be inspired to hop into bed.

2. Adrenaline Is Unleashed

When we kiss, our bodies jump into overdrive, and release a burst of adrenaline. "It’s like that 'fight or flight' response we have all heard about," Klapow says. "The heart rate goes up, muscle tension increases, our breathing rate speeds up, and blood flows to our internal organs."

It's why you might feel "weak in the knees." But this feeling also plays a role in assessing your chemistry. "It can leave you feeling less than satisfied, or feeling nothing," Klapow says, at which point you'll feel free to move on.

He points out, though, that since many first kisses are awkward — due to nerves and other factors — you might want to give it two or three more kisses, before you really know for sure.

3. All Your Brain’s Happy Chemicals Are Released

Not only is your body flooded with the feel-good chemical oxytocin during a kiss, but it is subject to a host of other happy chemicals, too.

"Kissing not only helps with serotonin and endorphins, that our body needs to elevate our mood, it also helps with boosting dopamine that regulates our sexual desire," Marla Renee Stewart, M.S., a sexologist, tells Bustle.

It's why a first kiss is so exhilarating, and why it so often leads to the desire to be even more intimate.

4. You Feel "Warm & Fuzzy"

Also thanks to oxytocin, you might get that "warm and fuzzy" feeling, which contributes to the sense that you're falling in love.

As you go in for a kiss, "oxytocin, aka the 'love hormone,' rushes through your veins," Dr. Tasha Seiter, Ph.D., M.S., MFTC, a relationship therapist, tells Bustle. "With oxytocin released from your pituitary gland and binding to receptors throughout your bloodstream, you feel instantly close and connected."

5. Your Pupils Dilate

Since a first kiss triggers your sympathetic nervous system, aka that fight-or-flight response, your pupils will dilate, too.

While it sounds strange, the pupils seriously widen whenever we feel intense sexual attraction, so if you’re kissing someone you are heavily digging, and want to know if they’re feeling the same way, check to see if their eyes are dilated, too.

Fun fact: this also might be one of the reasons we close our eyes when we kiss, because when our pupils are so open, it makes us susceptible to light sensitivity.

6. You Get "Butterflies"

Ever wonder why you get butterflies in your stomach during a first kiss? It has everything to do with that stress response.

"Your biological stress system is actually activated when you have your first kiss," Seiter says. "But, this doesn’t mean you’re stressed out. You’ll experience increased heart rate, sweating, or butterflies in your stomach; a physiological excitement response."

It's the nervous system at work again, which results in "biological fireworks," Seiter says, or the feeling of butterflies in your stomach.

7. Your Nerve Endings Become More Sensitive

Ever notice how a good first kiss becomes a full-body experience? As Klapow says, "The peripheral nerve endings become more sensitive, which is why you'll feel subtle touches or physical contact that you normally wouldn’t attend to."

It's why there's a rush of energy when your partner touches your back, or why the wind in your hair is electrifying. A kiss essentially makes your entire body hyper-aware — to the point you remember it for years to come.


Wlodarski, R. & Dunbar, R.I.M. Examining the Possible Functions of Kissing in Romantic Relationships. Archives of Sexual Behavior, 2013 DOI: 10.1007/s10508-013-0190-1


Dr. Josh Klapow, Ph.D., clinical psychologist

Marla Renee Stewart, M.S., sexologist

Dr. Tasha Seiter, PhD, M.S., MFTC, relationship therapist

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