Sexy Science by Dr Mairi MacLeod: Kiss and tell yourself all you need to know

EARLIER this week I went to see Gurinder Chadha's fun new movie, Angus, Thongs and Perfect Snogging, about 14 year-old Georgia Nicolson who is grappling with the all-important issues of getting a boyfriend and, obviously, doing tongue-tango with him.

Georgia and her mates devise a scientific snogging scale to document their progress: 1. holding hands; 5. open mouth kissing; 6. tongues; 7. upper body fondling, and so on.

As I remember I nearly reached level 6 when, at the age of 13, I got cornered by a guy at a party who was intent on shoving his tongue in my mouth. I gritted my teeth and resisted with all my might, I mean I really didn't fancy those multitudes of foreign bacteria sloshing around in my buccal cavity thank you very much. Although, funnily enough, it didn't take long for me to get a taste for it.

You've got to admit though, kissing is a pretty weird thing to do. Why do we like it and what's it for? This is what Susan Hughes of Albright College, Pennsylvania and her colleagues wanted to know, so they recruited 1,041 men and women and quizzed them in great detail about their smooching habits.

The researchers figured that we might use kissing as a way of assessing someone's suitability as a mate, after all we can tell a lot about someone's health by the state and smell of their mouth, and it turned out that women were especially particular about their partner having good teeth.

But we can also get vital information about the genetic compatibility of our snogging mate from the pheromones we inhale and taste. We tend to be attracted to people whose smell indicates that they are not too genetically similar too us, which will be a good thing should we end up having kids with that person. Women are more sensitive to such chemical cues and in the study reported that they were less likely than men to have sex without first kissing their partner.

Men seem to like to swap more spit and preferred wetter kisses. They could potentially, though unwittingly, get information about a woman's fertility through hormones in saliva, say the researchers.

The lips and tongue are among the most sensitive parts of the body, making kissing a sensual delight and triggering the release of feel-good chemicals and hormones such as oxytocin which induce emotional closeness. This brings us on to another potential function of kissing: bonding. In the study both men and women rated kissing as more intimate than cuddling, holding hands or caressing.

Some would argue that full-on kissing can be more intimate even than sex, which would explain why prostitutes generally avoid kissing their clients: it's a way of keeping emotional distance.

Both sexes agreed that kissing creates greater closeness with a long-term partner but, predictably, women felt kissing to be important throughout the relationship while men were more likely to lose interest over time.

Men and women also agreed that kissing after sex makes them feel closer but women were far more likely to initiate it. I guess this squares with the idea that men often want sex without commitment afterwards.

In fact, men tended to use kissing as a seduction device and Hughes and her co-workers speculate that men are particularly partial to wet tonguey kisses because they may be able to introduce hormones or proteins that make their partner more aroused.

Georgia is a bit young for all that, but she did resort to going for snogging lessons to hone her technique, which actually may have been a wise move, since it seems that the first kiss can make or break a relationship.

The researchers reported results of a survey asking the question: "Have you ever found yourself attracted to someone, only to discover after kissing them for the first time that you were no longer interested?"

59 per cent of men and 66 per cent of women answered "yes". Better make that first smacker a good one, then.

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