According to a 2013 study by researchers at Oxford University’s department of experimental psychology there are three reasons we kiss in a relationship: to assess how suitable a partner is, to help our relationship stay together and – not to put too fine a point on it – to arouse us. Sounds straightforward enough, except the science behind kissing is surprisingly complex, and involves a cocktail of bodily chemicals more powerful than anything in your medicine cabinet.

When we meet someone we’re attracted to, we are biologically driven to kiss because the closer our noses get to a potential partner’s body the better access we have to their pheromones – chemicals released from areas including the upper lip that emit a smell to attract the opposite sex.

“You can find someone tremendously attractive then get close to them and not feel a thing because their pheromones don’t do it for you,” explains Robert Page, creator of sex education film series The Lovers’ Guide. Our ‘signature smells’ are made up of proteins called the major histocompatibility complex (MHC) that regulates our immune system. Research suggests we subconsciously select partners with a different MHC to our own, so that any future children will develop immune systems that benefit from both.

Slip of the tongue

The idea that couples’ genes determine whether they’re destined for each other was actually spearheaded by Swiss biological researcher Claus Wedekind in 1995 with what is widely referred to as the “sweaty T-shirt” study. Men wore the same T-shirt for two days before women were asked to sniff the T-shirts and reveal which smell they were most attracted to. The results showed that, on the whole, women were most attracted to men with genes dissimilar to their own. And because genes can also affect how our brains interact, genetic compatibility is thought to be essential not only in ensuring we are attracted to our partner, but that our personalities gel as well.

As well as establishing each other’s scents, there are other very good reasons to pucker up. A passionate kiss on the lips triggers the release of a bonding hormone called oxytocin, along with the powerful neurotransmitter dopamine – a substance also stimulated by sex and class A drugs such as cocaine and heroin. “Dopamine helps us feel rewarded and experience pleasure,” explains Sheril Kirshenbaum, author of The Science Of Kissing: What Our Lips Are Telling Us. “It is responsible for the type of intense desire that makes a new romance feel addictive.” When that ‘spike’ of dopamine in the brain subsides, she says, it causes us to crave more and can even lead to a loss of appetite, insomnia or euphoria. So you can, quite literally, feel love sick.

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