What Exactly Causes Sexual Tension, Anyway?

Photographed by Refinery29.
You're sitting next to your crush when it happens — their leg brushes yours and no one pulls away. Suddenly, you can hear your heartbeat in your ears and every nerve in your body screams for you to just lean over and kiss them.
It's a moment you've likely experienced, and one that's easily described as "sexual tension." But what does that even mean? It's a concept that's hard to describe without talking about how it feels: butterflies in your stomach, every little hair on your arms standing up, sweaty palms. But what actually causes it and how do you define it? Can you even define it? (According to Merriam Webster, the answer is no.)
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Merriam Webster does have a definition of plain old "tension" though, describing it as "a state of latent hostility or opposition between individuals or groups." And that's pretty accurate when you're talking about sexual tension, too, according to Daniel G. Amen, MD, a psychiatrist and author of Change Your Brain, Change Your Life. Except the "groups" in this case are opposing areas of your brain.
Your prefrontal cortex (aka "judgement center") is duking it out with the pleasure centers in your brain over whether you should or shouldn't make a move. The more risk that's involved, the more these two areas of your brain will have to fight. If your crush is relatively low-risk (like someone who you already know finds you attractive because they swiped right, for example), then the tension might be fleeting. But if you've been longing after a friend or someone who's already in a committed, monogamous relationship, then there's much more risk involved — and a lot more tension.
In cases like these, sexual tension could actually save you. "If you don’t play it out in your head, then disaster is waiting for you," Dr. Amen says. So go ahead and thank your prefrontal cortex for all of the bad relationship moves you didn't make.
Does that mean we can just define sexual tension as the pesky voice of reason in your head and move on? Kind of, but thinking of it as something that stops you from doing what you truly want would be a disservice, because the judgement center and the pleasure center of your brain don't just battle it out over someone who's decidedly terrible for you. Sexual tension can be a positive thing.
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Remember how amazing it can feel when you finally kiss the person you've been playing knee hockey with for months? The bubble of sexual tension that's been building bursts and you're flooded with the happiness of knowing that making a move wasn't so risky after all. That's a beautiful feeling, and one that only exists because sexual tension rustled the butterflies in your stomach in the first place. If you're lucky, you'll have moments of sexual tension throughout a long-term relationship.
How is that possible with the will-we-or-won't-we risk off the table? Because the question of whether or not your crush likes you back is just the big risk — not the only one. "Maybe the momentary release goes away," Dr. Amen says. "But I’ve been a psychiatrist for 35 years and let me tell you, there are a lot of people in lasting relationships who still have the hots for each other."
That's because relationships are full of little risks, too. Will your partner think the lingerie you bought is sexy? Will you get over your first big fight? Will your partner be interested in changing things up during sex? All of these moments reawaken the sexual tension between you, and provide plenty of opportunity for it to be released.