We've known it since grade school: Kissing transfers germs that can pass along colds or the flu. But according to Dutch researchers, the 80 million or so bacteria exchanged during just ten seconds of a kiss has real, measurable upsides, including measurable stress release, stronger immune systems, and even a build-up of good bacteria.
Lead researcher Remco Kort and his colleagues had 21 couples fill out a questionnaire, provide saliva samples before and after a kiss, then eat yogurt with markers to count the number of bacteria transferred. They found that microbes exchanged on the tongue not only survive, but that couples that kiss a lot also begin to share a similar makeup of gut bacteria compared to individuals who'd never kissed at all.
"It's healthy to kiss," says Kort. "If you look at it from the perspective of diversity, you're exposed to many bacteria, and this major exposure will increase your resistance." This bacteria, he explains, helps fight disease-causing microorganisms in the same way as eating a healthy diet full of veggies and probiotics from yogurt, embracing outdoor germs, or avoiding overexposure to antibiotics. Like the bacteria given to us by our mothers at birth or the germs we pick up through experiences throughout our lives, kissing gives our microbiomes a wholesome color.
But if you still find the idea of germs repulsive, there's another reason why we kiss and probably will continue to throughout our lives: it makes us feels good. Research shows a 15-minute make out session can boost a man's oxytocin level (the brain chemical that promotes strong feelings of emotional attachment, which helps couples bond), and lower their cortisol level (the hormone related to stress). Then there's the release of dopamine, the chemical associated with pleasure and reward. When you kiss someone, the sensitive nerves along your tongue and lips fire signals up to your brain, prompting a flood of dopamine that gives you a natural high (Dopamine has also been linked to addiction, which could explain why a few seconds into a kiss leaves you craving more.) Think of it as a mini orgasm, since the same brain chemistry is thought to be at work when you climax. French kissing could also be the best start to foreplay, since psychologists have suggested men use the move to successfully increase sexual arousal, while women use it to decide whether or not the session is worth continuing.
But of course kissing can still be a germ problem when you're careless, leading to infections like mono or hepatitis. But experts say you shouldn't be overly concerned about the germs. "When you first hear 80 million, it sounds surprising," says Dr. Gail Shust, an infectious disease expert at Mount Sinai Hospital. "But we've been kissing since the beginning of time, and it doesn't seem to have held us back."
And in two healthy partners, Kort says there's no need to be overly paranoid. "Of course you can potentially pass diseases through kissing in the same way that certain things can be passed through respiratory secretion," Dr. Shust adds. "But if you just have a typical cold or viral illness, most of the people you're intimate with anyway have probably already been exposed to it, so you're not putting them at increased risk."
As for the idea that you should kiss more people for the health of your microbiome and immune system, Shust thinks that's a bit of a stretch. "It's true that everybody has bacteria in their mouths that help maintain a certain homeostasis," she explains. "But they only studied 21 couples so this needs to be looked at more before we can make some great generalization." For now, Shust suggests we continue to kiss our partners to show affection and reap all of the emotional and feel-good benefits that come with it.
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