Smooching, snogging, pashing, kissing - whatever you call it, there's no denying that swapping spit is pretty damn enjoyable. But how much do you really know about kissing? To celebrate National Kissing Day, here's a few factoids to think about next time you put your tongue in somebody else's mouth.

#1 - During a kiss you exchange over 5 million bacteria

No matter how careful you are about where the person you're kissing's mouth has been, you're still set to exchange up to 280 colonies of bacteria and more than 5 million individual bacteria during a particularly length snog.

#2  - But snogging actually help your teeth stay cleaner

Besides releasing dopamine, the chemical that makes you feel like you're on cloud nine, snogs can actually be good for your oral hygiene. Yep, it's been argued that those bactrria entering your mouth can act a bit like an impromptu teeth cleaning, flushing away plaque and bacteria from your mouth.

#3 - How you kiss might actually be determined in the womb

It's been suggested that the side you naturally tilt your head to kiss is actually something that's determined before you are even born. Over two-thirds of us apparently naturally tilt our heads to the right, something that scientists argue comes from a development in the womb, where fetuses most often naturally tilt their heads to the right to fit into the tight space.

#4 - Kissing involves a serious facial workout

Forget hitting the cross trainer as your face deserves some serious recognition for the effort it goes through to kiss. Scientists researching kissing at University College London (WHAT a job) found that kissing requires 146 muscles in the face to work together. That includes 34 facial muscles and 112 postural muscles, which are those found in the rest of the body.

#5 - making out burns calories

Speaking of workouts, kissing really does burn calories. In fact a quick kiss will burn between two and three calories while a full-bodied snog should blitz between five and six. That said, a full minute long kiss could burn up to 26 calories.

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