12 Shocking Things No One Ever Taught You About The Saliva You Swap When Kissing

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When you're in the middle of a kiss, the last thing you're likely to think about is the other person's saliva, much less what may or may not be transferring between you. But turns outs there's a whole lot going on inside our mouths, and it can make the act of kissing even more interesting than you might think.

"The human body is an incredibly complex, contained, self-sustaining ecosystem of chemicals and micro-organisms," sex expert and educator Candice Smith, M.Ed., tells Bustle. "While we may discount it as 'spit,' our saliva contains the building blocks, the real chemical essence, of who we are." And when you kiss someone, that essence is shared.

"Your saliva is you, distilled into fluid form," Smith says. "When we kiss, we’re essentially sharing a tiny bit of our ecosystems — we’re swapping genetic information that our bodies unconsciously process — and in doing so, we learn more about each other in an instant than we ever could consciously."

That's why you may not be sure, in a romantic sense, that you really like someone until you kiss. "That’s what makes it such a powerful form of intimacy; when (if) you decide to continue swapping saliva, you’ve essentially selected each other not just on a conscious level, but you’ve accepted them with every fiber of your DNA, too," Smith says. Read on for more interesting things no one ever taught you about swapping spit, according to experts.


Kissing Can Boost Your Immune System

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With a single kiss, you're coming in contact with up to 80 million bacteria. And in doing so, it may help strengthen your immune system, so you're less likely to catch colds.

"Children initially build up their immune resistance to the world by interacting with it," Smith says. As kids, we put everything — germy or otherwise — into our mouths and don't think twice about it. But that habit lessens, for various reasons, as we grow up.

"We don't do that quite as much as we get older, so kissing may be one of our more effective ways of introducing our immune systems to new microbiomes of bacteria," she says. Without even trying, kissing could be making you healthier.


It Can Transfer Testosterone

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If you're kissing a male, they could be transferring some of their testosterone to you, Smith says. And that can make you more attracted to them. "Testosterone is an anabolic sex hormone that can incite sexual drive, so scientists theorize that unconsciously, your testosterone-producing partner may be trying to get you in the mood." Pretty interesting, right?


It Serves As A "Bacterial Litmus Test"

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When kissing someone, your body is assessing your chemistry via their saliva. "Getting a French kiss from someone is like giving them a bacterial litmus test — your body's microbiome can immediately tell whether or not their germs are in tune with yours," Smith says. "If they don't harmonize, your body will reject that partner as a possible mate." And you won't be into the kiss at all.


Spit Makes You Saltier

When you kiss, enough salt is transferred in the process that you technically become saltier, by about 0.45mg, Smith says. "The amount of saliva obtained from your partner during an average kiss also contains 9mg of water, 0.7 mg of fats and 0.7 mg of proteins."


You Can Swap Morning Breath

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As Smith says, "Morning breath can be transferred through saliva." So if kiss someone who just woke up, be prepared to feel a little less fresh.


You Might Drool

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You know how your mouth waters right before you eat? The same thing can happen right before you kiss. "Knowing we're going to kiss literally makes us drool," Smith says. "Research shows that anticipation of a kiss activates the salivary glands."


Kissing Can Be Good For Your Teeth

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The excess saliva that's produced right before a kiss can even, in some small way, be good for your dental hygiene. "A kiss a day won't keep the dentist away," Smith says. "But the sudden increase of saliva in your mouth before a kiss 'flushes' out the stagnant bacteria responsible for tooth decay."


Saliva Can Play A Role In Choosing A Partner

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When you kiss, "your evolutionary mapping uses the DNA and other genetic information exchanged [...] to decide whether or not you want to have sex with the person on the other side," Mark Burhenne, DDS, founder of, tells Bustle.

And research suggests it can help you choose whether or not you want to proceed. "Women who are currently fertile are even more likely to select a sexual partner based on what they glean from saliva," Dr. Burhenne says.


Your Spit Will Taste Different During Your Period

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During your period, your saliva (and therefore your kisses) can actually taste different compared to times of the month. As Smith says, "That's because the brain produces different levels of sex hormones such as estrogen, oestrogen, estradiol, and progesterone as you go through your cycle, and these hormones affect your body's biochemistry drastically, including your breath odor and the chemical composition of your saliva."


Kissing Reduces Stress

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If you've ever felt relaxed after kissing, you're definitely not alone. "Kissing literally reduces stress," Smith says. "Saliva samples taken after extended periods of kissing revealed reduced cortisol (the stress hormone) levels."


It Helps You & Your Partner Bond

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Kissing also helps you bond with your partner, due to fact it releases oxytocin, or the "love" hormone. Saliva samples have shown higher levels of oxytocin after kissing, Smith says, which boosts feelings of affection and attachment.


It Can Impact Your Dental Health

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"Exchanging saliva also has huge implications for the oral microbiome," Dr. Burhenne says. "You trade oral bacteria when you kiss intimately, meaning that you'll take on some of your partner's oral microbiome."

So if they have issues with their teeth, it may impact you. "If you're used to eating a lot of sugar and not brushing frequently, this might not be a huge deal — but if you're a healthy eater with strong teeth, and your partner isn't, you may be risking loading up your oral microbiome with shady bacteria," he says.

Whether it's boosting your immune system, or giving you morning breath, kissing has a lot more going on than meets the eye.