The Science of Kissing: 5 ways our lips can seal the deal for romance

This Valentine’s Day will see plenty of couples moving in to offer each other a kiss. Kissing, in one form of another, is practised in just about every society and culture. Until recently, no one has ever studied why we do it. Here’s a look at what scientists are beginning to learn about the art of kissing.

1. We were made for it

Most animal species do some kind of nuzzling with their offspring or mates. Some chimpanzees will go further to press their lips together in what we might think of as kissing, but only briefly. Yet revelling in “long, slow, deep, wet kisses,” as the character Crash Davis in “Bull Durham” called them -- well, that’s uniquely human.

Sheril Kirshenbaum writes in The Science of Kissing: What Our Lips Are Telling Us that humans are the only creatures in the animal kingdom that have lips made for kissing. Unlike other primates, our lips are “everted,” meaning they purse outward, which makes them perfect for soft kisses.

What’s more, our everted lips are packed with sensitive nerve endings. Lips are thin-skinned and are one of our most exposed erogenous zones.

Read a preview chapter: The Science of Kissing

2. It’s all about chemistry

Moving in close to lock lips with someone we love causes us to release chemicals that ease stress.

While the first kiss of new love causes a rush of stimulating hormones, kissing among long-term couples is vastly different. Kissing releases waves of soothing hormones such as oxytocin, the “bonding” hormone that women produce during childbirth and breastfeeding.

In a 2007 study, psychologist Wendy Hill at Lafayette College in Pennsylvania and her team tested the stress levels of several college-aged male-female couples and then had them either kiss together for 15 minutes or hold hands and listen to music. The researchers then measured the participants’ hormone levels again.

They found that both men and women had a decline in the key stress hormone cortisol after their kissing session -- suggesting their stress levels had fallen.

In men, levels of oxytocin actually rose. Among the women, oxytocin levels actually fell, though the authors suspect that might have had something to do with the awkwardness of the clinical research lab setting.

Read it: Oxytocin hormone promotes bonding

3. Sensing a good match

Kissing may be nature’s way of letting us use our senses of taste, touch and smell to gather all sorts of information about our partners. Whether we realize it or not, we then use that info to decide if this is something we want to pursue further. In that way, biologists say kissing among humans may be similar to the sniffing that animals do to each other when they meet.

Psychologist Gordon G. Gallup, Jr., from State University of New York at Albany says kissing might even be some of kind of evolutionary holdover that helps us “sniff out” bad, incompatible mates and thus avoid reproducing with someone with would be genetically a bad match.

As anyone who has ever had a disastrous first kiss knows, that first kiss can be a deal-breaker. Gallup found in a survey he conducted several years ago that 59 per cent of men and 66 per cent of women said they had nixed a budding relationship because a kiss had gone badly.

Study: Sex and the nose: human pheromonal responses

4. Signals for sex

Passionate kissing has been shown to cause all sorts of physiological responses: racing pulses, increases in respiration, and surges in dopamine -- the hormone involved in craving and desire.

For many people, particularly younger couples, the kiss sets the stage for sex.

Prof. Gallup participated in a larger survey of more than 1,000 college students a few years ago along with Susan M. Hughes, and Marissa A. Harrison, to ask college students about why they kiss. What they found wasn’t far off from we might think of as the stereotypes of men and women looking for love and sex.

For the most part, the men in the study were more likely than women to report they used kissing as a means of gaining sex. Women on the other hand, were more likely to say they liked to kiss to establish intimacy as well as to monitor the status of their relationship.

Women were more likely than males to insist that kissing had to come before sex, and to emphasize that kissing was important during and after sex too.

About half the men said they would be perfectly content to have sex without kissing, while only one in seven females would consider sex with someone without kissing them first.

Study: Sex Differences in Romantic Kissing Among College Students: An Evolutionary Perspective

5. Keeping a partner

While kissing has its uses in sex and foreplay, for many couples, kissing is an essential part of maintaining intimacy in their relationship.

One online survey of 900 participants conducted by Oxford University experimental psychology researchers Rafael Wlodarski and Robin I. M. Dunbar found that how often couples kissed was significantly related to their relationship satisfaction -- even more so than the frequency of sex.

The researchers said that suggests there’s something unique about romantic kissing that affects attachment and relationship satisfaction more than sex does.

Another study from the Kinsey Institute found that it’s not just younger couples who enjoy kissing; so do seniors. The study surveyed older couples from five countries around the world and found that cuddling and kissing were important ingredients for long-term relationship satisfaction, no matter where the couples were from.

Men and women in the study were likely to report sexual satisfaction if they also reported frequent kissing and cuddling, sexual caressing by the partner, suggesting that how often couples kiss is often a good measure of the strength of their connection.

Study: Examining the Possible Functions of Kissing in Romantic Relationships