Things About Kissing You Probably Never Wanted To Know

Kissing is a weird, wonderful, and almost exclusively human trait. Yes, some primates kiss but, interestingly, not all humans do. Research found that just 46 percent of cultures throughout human history have engaged in romantic kissing. In societies that have developed a "taste" for kissing, though, people have definitely worked hard to master it. After all, kissing is complicated. You use up to 146 different muscles when you kiss. We also spend a large portion of our lives kissing — 20,160 minutes (14 days) on average.

Of course, this time is well spent because kissing is incredibly pleasurable. In fact, our lips are actually one of the most sensitive spots on our bodies (even more sensitive than other areas), with up to 10,000 individual nerve endings. Still, as amazing as a good kiss can be, there are some disturbing things you may not be aware of that happen when we kiss— things that only happen when two individuals press their lips together in a sexy yet sloppy passionate exchange of saliva. Read on to find out everything you probably never wanted to know about locking lips.

There's a reason humans are seemingly born knowing we should shut our eyes during a kiss. And it's not just good manners or fear of the person we're kissing staring back from just a couple inches away. No, the actual reason we kiss with our eyes shut is because kissing is so stimulating, our brains have a hard time processing a passionate kiss when we do it with our eyes open, a study in the Journal of Experimental Psychology has suggested.

Researchers in the U.K. had 16 volunteers complete a series of puzzles that involved searching for specific letters. While they were completing the puzzle, the scientists delivered a brief random vibration to their hands. The more demanding the puzzles became, the less likely the volunteers were to notice the vibration.

This finding implies that reducing visual demands by shutting your eyes may improve tactile awareness, which could also help you feel a kiss more intensely, cognitive psychologists and co-authors of the study Polly Dalton and Sandra Murphy told The Independent. Keeping your eyes shut also blocks out other distractions, leaving the brain with more capacity to focus on the kiss, she said.

Here's a visual you never wanted: A 10-second kiss can spread as many as 80 million bacteria from one person's mouth into the other, according to a study published in the journal Microbiome. Researchers in the Netherlands made the shocking discovery after studying the kissing behavior and levels of bacteria within the bodies of 21 couples. First, the researchers surveyed the individuals and found how often they kissed each other. Then they swabbed their mouths and compared levels of bacteria. The results revealed that the more often the couples intimately kissed, the more similar the levels of bacteria in their mouths became.

To further test these findings, the researchers then tasked one person from each couple with drinking a probiotic shake containing specific trackable bacteria. After the couples kissed for 10 seconds, the scientists measured the bacteria levels within the mouths of the people who'd received the kiss. "We wanted to find out the extent to which partners share their oral microbiota — and it turns out, the more a couple kiss, the more similar they are," the study's lead author Remco Kort confirmed to Science Daily.

In an era in which many are concerned about the spread of COVID-19, you may wonder about the safety of kissing. Although we often think of respiratory droplets being expelled during a cough or a sneeze, kissing puts you into direct contact with those droplets, and is thus a way coronavirus can be spread, the Mayo Clinic has warned. However, kissing may not increase your risk for the common cold or flu.

"The common cold virus travels in the mucus from the respiratory system, so unless you have a bad cough, and some of the respiratory mucus has made its way into your saliva, the cold virus will not be transmitted by kissing," Professor Ron Eccles, director of the Common Cold Center at Cardiff University, told HuffPost.

Similarly, in a review of viruses spread through kissing, European physicians concluded "it is unlikely that kissing could constitute a route for transmission" for the virus that causes influenza. In the case of both colds and the flu, experts say that it's important to keep your hands clean. "Your fingers can easily become contaminated with viruses by holding hands with someone who has coughed or sneezed into their hands, or by touching door handles in public places," Eccles said.

There's a reason people call mononucleosis (or mono) "the kissing disease." Although there are other ways to catch the virus — sharing utensils or glasses or coming in contact with infected nasal fluids, blood, or semen — a primary mode of transmission is through saliva. This is why it is easy to catch through kissing. All it takes is coming into contact with a bit of infected saliva, and there's a good chance you'll become infected.

Transmission occurs incredibly easily — so easily, in fact, that more than 95 percent of Americans will develop mono at some point during their lifetimes, Dr. Todd Wills, an assistant professor of infectious diseases and international medicine at the University of South Florida, revealed in an ABC News article. While 50 percent of children are infected with the virus before the age of five, it doesn't only affect children.

People of all ages can develop mono and, like chicken pox, once the virus is in your system, it's there forever. Symptoms of mono can include fatigue, sore throat, fever, swollen lymph nodes in the neck and armpits, swollen tonsils, headaches or rash, and extreme fatigue that may last for several months (via The Mayo Clinic).

There may be a reason older couples can finish each other's sentences after spending years together kissing and cuddling. Science suggests the brain can actually start to sync with the brain of your partner when you share a kiss. And the more you enjoy the kiss, the greater the synchronization can be. This is great news if you're looking for someone to spend your life with, but perhaps not welcome information if you're just sharing a kiss in a casual relationship.

Researchers in Germany reported on the brain syncing discovery in a study published in the journal PLOS One. In the study, the researchers had a group of 15 couples kiss repeatedly following different tasks. Their brains were scanned throughout the length of the experiment, following each kiss. The result: When the couples kissed, their brain activity spiked and became more harmonious. "I would suggest that kissing synchronizes our brains to produce a state or conditions for a better understanding of each other — or for getting in the right mood for partner-oriented behavior," the study's co-author Viktor Müller told the University of California, Berkeley's Greater Good magazine.

The secret to longevity could be getting in plenty of kisses with the person you love. When researchers in Germany spent two years studying the lives, careers, and personal habits of a group of men, they found that individuals who kissed their spouses every morning before leaving the house were sick less often, were involved in fewer car accidents, earned higher salaries, and even lived an average of five years longer than individuals who didn't kiss their spouses regularly (via Psychology Today). Rather than the power of love helping these men to do so well, scientists speculate that kissing your spouse in the morning increases confidence and helps you start the day in a positive way. 

A separate report by Indiana's Kinsey Institute supports this idea. In their survey of over 1,000 couples who had been together an average of 25 years, they found that couples who kissed and cuddled most frequently were also the happiest and most satisfied with their lives overall. 

The success or failure of a relationship may be impacted by how often a couple kisses. The finding comes from a paper published in the Archives of Sexual Behavior. To study the importance of kissing within long-term relationships, researchers analyzed data collected from 1,605 individuals in committed relationships of at least two years. In addition to studying how often the individuals reported kissing their significant other, the study's authors also analyzed how frequently the individuals were aroused, their level of arousal, and their overall sexual satisfaction within their relationship.

The result: The more frequently individuals kissed their partner, the higher they rated their satisfaction with both their sex life and their relationship as a whole. "Kissing can be a useful tool in helping the emotional and sexual aspects of relationships grow stronger," the study's author Veronica Hanna-Walker told PsyPost. In addition to increasing levels of sexual arousal and increasing the likelihood of orgasms during sex, kissing also helps partners to form a closer bond and grow more attached to one another, she said. "Kissing is a small part of romantic relationships, but it is important to not forget it."