With Valentine’s Day looming at the end of this week (well, looming for those who have not yet given sufficient thought to cards, flowers and chocolates–I’m looking at you, fellow members of my gender), it seems a good time to revisit the science of kissing.
And just in time for Valentine’s, new research on the topic is being reported at the annual conference of the American Association for the Advancement of Science this week in Chicago.
Before we get to that, a quick refresher on why we engage in a practice which involves the exchange of, by one estimate, 278 colonies of bacteria per osculation.
One theory is that kissing may have evolved as a means of unconsciously testing the fitness of a potential mate. On the grand scale, it could be a way of checking for genetic compatibility: research has shown, as I wrote a few years ago, “women subconsciously prefer the smell of men whose genes for a particular class of immune systems proteins are different from their own–presumably because offspring from such a match would have a stronger immune system, and hence a better chance of survival, than offspring from other men.”
Or maybe it helps mate-selection far more prosaically. Psychologist Susan Hughes, co-author of Sex Differences in Romantic Kissing among College Students: An Evolutionary Perspective, says, “Females place a lot more importance on the breath and teeth of a person. This shows how well you care for yourself and your hygiene and women are a lot more picky when it comes to that.”
While there’s no doubt that kissing helps us select mates–if a first kiss goes badly, there may be no saving the relationship–we also do it (especially those of us who have already selected our mates) because it feels good. Lips and tongues are packed with nerve endings. And then there’s chemistry…which is where the new research comes in.
Wendy Hill, a professor of psychology at Lafayette College in Pennsylvania, tested the levels of two hormones, cortisol and oxytocin, in 15 couples before and after they held hands and kissed. They found that kissing reduced the level of cortisol, which is a stress hormone, in both sexes. To their surprise, however, they found that levels of oxytocin, a hormone involved in social bonding, rose in the men, but fell in the women.
Working on the hypothesis that the rather cold and antiseptic environment of the lab in which the tests were conducted had something to do with that, they replicated the test in more intimate surroundings, complete with romantic background music…and found that women do indeed get more out of a kiss when the ambience is more amenable to amore.
“This study shows kissing is much more complex and causes hormonal changes and things we never thought occurred,” says Hill. “We tend to think more about who we are kissing and how it feels, yet there are a lot of other things happening.”
Precisely why kissing triggers these hormonal changes isn’t well understood. Some scientists believe pheromones are involved: chemical messengers known to be important in other mammals when it comes to attracting mates.
That’s not a universally accepted explanation, because we do not, as far as we know, have pheromone-detection organs. However, some scientists believe we can detect them with our noses.
Even admitting that kissing is both pleasurable and helpful in selecting mates, though, is it actually healthy? What with the exchange of bacterial colonies and viruses and bits of whatever each partner last ate?
Well, we’ve already noted that it reduces the levels of the stress hormone cortisol. That certainly has health benefits.
But even the exchange of germs may, as well. Helen Fisher, a professor of anthropology at Rutgers University in New Jersey and author of the book Why We Love, notes that, “If you’re sharing your germs with somebody, you’re boosting your internal defense system.”
Combine all this with research that says that dark chocolate is good for you, and the soothing effects of floral fragrance, and Valentine’s Day may well be the healthiest holiday of the year.
Unless you forget all about it, guys. Then it may be the most dangerous of all.
