Why do we kiss? And does it have any health benefits?
While many of us love a good smooch, for some the sight and sound of kissing (we blame you Love Island couples) is enough to bring on the, er, ick.
If we pause and think about the act itself, you might consider swapping saliva is a rather odd way to express your affection for someone - particularly when research reveals just one 10 second kiss can transfer 80 million bacteria. Double ick!
But, before you vow never to lock lips ever again, it's also worth noting that there are a whole wealth of health benefits involved in a good smacker.
We've crunched the science to share why we actually kiss and some of the health-boosting plus points of puckering up.
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Why do we kiss?
While in the UK kissing is considered a normal way to show your partner you care, you might be surprised to learn that it isn't the done thing everywhere.
In fact around half of cultures worldwide do not actively engage in “lip-to-lip contact”.
After looking at 168 cultures, scientists from the University of Nevada in Las Vegas found just 46% displayed “the romantic-sexual kiss”, debunking the theory it is the universal way to show affection everywhere.
The team found the more “socially complex the culture”, the “higher frequency of romantic-sexual kissing”.
They noted communities in Sub-Saharan Africa and New Guinea, as well as Amazonian foragers, did not appear to engage.
Meanwhile as recently as 2014, the indigenous Mehinaku people of Brazil reportedly found kissing “gross”.
While this particular research suggests it is a relatively recent method of affection, Hindu Vedic Sanskrit written more than 3,500 years ago reportedly mentions kissing, hinting it has long been “acceptable” in certain communities.
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To uncover the reasons behind why we kiss, scientists turned to animals.
The BBC reports chimps kiss after conflict as a form of reconciliation, which is not considered romantic.
Bonobos, also known as pygmy chimpanzees, get affectionate more often, even using tongues.
The great apes are the only non-human animal to have been observed engaging in tongue kissing, with no other animals thought to share saliva.
This is said to come down to animals acute sense of smell, with everything from boars to spiders “sniffing” out pheromones as a sign of fertility.
But with a human’s sense of smell not as sharp, scientists from the University of Oxford found many turn to kissing to assess a potential “mate”, with some experts believing the act may simply be a socially acceptable way of getting close enough to detect someone’s pheromones.
It is also thought to “bolster” bonding between a romantic pair, while a further theory explores the idea that kissing is a sign of commitment, with people showing their partners they are willing to catch infectious conditions like flu to be close to them.
Interestingly, however, the findings of this particular research showed very little evidence to support the hypothesis that the primary function of kissing is to elevate levels of arousal.
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Is kissing good for us?
With many infectious pathogens lurking in saliva, kissing a sickly lover undoubtably puts you at risk, but puckering up with a healthy person, however, could do you the world of good.
Scientists from the Netherlands Organisation for Applied Scientific Research looked at 21 couples, with one member of each pair being given a probiotic yoghurt drink.
The couple then enjoyed an “intimate kiss”, with bacteria counts on their tongues measured before and after.
The scientists “identified the probiotic Lactobacillus and Bifidobacterium bacteria” moved over to “most kiss receivers”.
During a 10 second kiss, the “total bacteria transfer” was averaged at 80 million bacteria. But high levels of “good bacteria” have been shown to boost our immune system, helping fight off disease, so the bacteria swap can work both ways.
“Rather bizarrely, research has shown that the bacteria that you share with your partner during a kiss can actually help to boost your immune system,” an expert from mydentist previously told Yahoo UK. “Studies carried out in the Netherlands in 2014 found that 80 million bacteria are transferred during a ten-second kiss, and rather than making us ill, this can actually help to boost our body’s defences.”
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And the benefits do not stop there.
Japanese medic Dr Hajime Kimata won a scientific Nobel Prize for his research on how smooching may ward off allergic reactions.
He looked at 30 people with eczema, 30 with allergic rhinitis - a runny nose caused by allergens - and 30 healthy volunteers.
The participants were exposed to their “triggers”, dust mites or Japanese cedar pollen.
Both before and after exposure, they were told to kiss “freely for 30 minutes with their lover or spouse alone in a room”.
This was found to significantly reduce the development of allergic wheals, red swollen marks on the skin.
It also lowered levels of inflammatory protein markers typically released during an allergic reaction.
Other health benefits of kissing
Helps keep your heart healthy
A good smooch can help keep your blood pressure and cholesterol level low. “One of the outcomes of a good kiss, is that our blood vessels dilate, bringing blood pressure back down to where it should be,” explains Zoe Coetzee, a relationship psychologist and matchmaking specialist previously told Yahoo UK.
A study of cohabiting and married couples found an increased frequency of kissing lead to decreased stress, increased relationship satisfaction, and decreased cholesterol levels. And since stress is a well-known risk factor for heart disease, kissing can help to keep your ticker healthy.
Makes you happy
A good lip-lock prompts the brain to release a happy little mix of feel-good chemicals like dopamine, which is responsible for feelings of desire and bonding, serotonin that elevates your mood and oxytocin. “Dopamine is associated with the feeling of reward and elation, and this has been shown to spike during a kiss,” explains Coetzee.
“Science has proven that serotonin, which is responsible for balancing your mood is also released when kissing. A deficiency in serotonin can lead to depression and it is an important chemical in regulating wellbeing. This heady mix, designed to make you feel good and want more, is all the more reason to invest in kissing time.”
Kissing is also known to help people “unwind” before sex, making it more comfortable for a woman and easier for both participants to climax.
Read more: How to get the spark back in a relationship
Tones your facial muscles
While a quick peck uses only a couple of facial muscles, a vigorous snogging sesh engages between 23 and 34 facial muscles—plus more than 100 others in the body.
So if you fear you’re beginning to suffer from saggy jowels, try tightening things up with some regular vigorous kissing.
Improves oral health
A kiss a day keeps the dentist away. Well, in a manner of speaking. Kissing increases saliva production and this saliva washes away bacteria that can cause cavities, tooth decay, and plaque build-up.
“The main benefit of kissing is that it produces more saliva in your mouth," explains Dr Khaled Kasem, Chief Orthodontist of European leading orthodontics chain Impress.
"Saliva is important because it helps you chew, taste, swallow, fights germs in your mouth and prevents bad breath - which is definitely not ideal when kissing!"
Saliva also neutralises the acids that sit on your teeth which helps to reduce your risk of getting tooth decay.
"With that extra saliva in your mouth, it can wash away the bacteria off your teeth, which breaks down stubborn oral plaque. So, in short, keep kissing if you want nice breath and healthy teeth.
"We would recommend kissing for four minutes in total each day to improve your oral health. But make sure to keep brushing and flossing as well to avoid spreading any germs during your kissing routine!”
But it's worth noting, says Dr Kasem, that you should probably avoid kissing when people are sick, have a cold sore or already have bad oral health hygiene. "Other than that, kiss away!" he adds.