It's International Kissing Day 2016 (yeah, apparently that's a real thing), and everybody's thinking about smooching. From Romeo and Juliet to Snow White and the Seven Dwarfs, pop culture has long upheld the mouth-to-mouth kiss as the pinnacle of sexual expression.
Yet it turns out sensual snogging isn't quite as universal (or as romantic) as we've been raised to believe. Here are four facts about kissing that Ryan Gosling movies never taught you.
1. Romantic kissing isn't "normal" in most cultures.
According to a 2015 study by research scientist Justin Garcia at Indiana University, only 46% of 168 distinct cultures surveyed around the world kiss on the mouth in a romantic way. Although most of Europe and the Middle East like to smooch, practically no indigenous cultures in Central America or sub-Saharan Africa offered researchers any evidence they enjoy making out.
2. Swapping saliva transfers 80 million bacteria in just 10 seconds.
It's obvious that swapping saliva with your partner means exchanging some of the gnarly little microbes living in your mouths. But scientists at the Micropia Museum of Microbes and the Netherlands Organization for Applied Scientific Research studied the kissing habits of 21 couples and found couples who shared nine kisses a day had remarkably similar oral bacteria.
After an open-mouthed smooch, the kissers had around three times the amount of probiotic bacteria in their saliva. The researchers estimated that around 80 million bacteria are transferred by kissing for just 10 seconds.
So if you're looking to get sick, snogging a sniffly partner may be the best way to catch all those germs in one swoop. A study by the British Medical Journal even suggested that teens who kissed multiple partners quadrupled their chance of catching meningitis.
3. Female kissing partners are subconsciously tasting and sniffing your hormone balance.
"Our sense of smell has a really strong role in how we choose a partner," scientist Sheril Kirshenbaum, author of the book The Science of Kissing: What Our Lips Are Telling Us, said in a phone interview. "Especially for women, who have a stronger sense of taste and smell, they place a lot of value on taste, scent and oral hygiene."
The sense of smell is connected to the immune system and sweaty body odor is especially reflective of a person's hormone levels, meaning the brain uses smell to subconsciously determine one's genetic capacity. If the other person's immune system seems likely to produce strong, healthy children, the subconscious brain will translate that into "totally kissable."
Kirshenbaum said that the rush of the chemical dopamine through your brain during a kiss actually makes your pupils dilate. The increased light sensitivity instinctively encourages people to close their eyes and focus more intensely on other senses, like taste and smell.
4. Men's kisses mess with your hormone balance.
Cisgendered men have extremely small amounts of testosterone in their saliva. This means if a dude is kissing the same person over weeks and months, it could potentially increase their partner's libido. (This might be especially true if the man is kissing a cisgender woman, as women are more sensitive to increases in testosterone.)
Biological anthropologist Helen Fisher told Wired that men who like messy, open-mouth kissing are probably "unconsciously trying to transfer testosterone to trigger the sex drive in women."
Basically, kissing is one of the most bizarre biological phenomena ever. But even though it's pretty weird, it still feels great.