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Chuck Zovko/Lafayette College

Two Lafayette College undergraduates kiss for research by neuroscience professor Wendy Hill (second from right) and her student research assistant, Evan Lebovitz (right).  Hill and Lebovitz presented their findings on how kissing affects hormone levels at the AAAS annual meeting in Chicago.

Chemical attraction: The science of kissing

by Beth Furtwangler
Feb 14, 2009

For the couples locking lips for the first time, what determines if sparks will fly? It’s all about the chemistry.

“When you kiss an enormous part of the brain becomes active,” said Helen Fisher, a research professor of anthropology at Rutgers University in New Brunswick, N.J.

She spoke Friday on the topic of the science of kissing, or philematology, as part of an aptly timed Valentine’s Day panel at the annual meeting for the American Association for the Advancement of Science in Chicago.

There are four temperaments, or biologically based traits, associated with different chemical systems in the brain, Fisher said. She looked at the dating choices of 28,000 people on the online dating site to determine how individuals’ primary temperaments influence who they are attracted to.

“Indeed, these chemical systems do make a difference in mate choice and attraction, Fisher said. “It now appears we are drawn to people who have fit particular biological profiles.”

What’s more, kissing releases chemicals that reduce stress hormones, said Wendy Hill, a neuroscience professor and provost and dean of the faculty at Lafayette College in Easton, Penn.

In her study, Hill had 15 heterosexual couples enrolled at Lafayette either kiss or hold hands for 15 minutes. Before and after, Hill measured their levels of oxytocin, the hormone associated with social bonding, and cortisol, which is linked to stress.

In the kissing group, both sexes had declines in cortisol and males had increased levels of oxytocin. The females’ oxytocin levels decreased, which Hill said was “very surprising,” but may be because the experiment’s setting was the student health center, and the participants were not completely comfortable.

The experiment was replicated in a “more romantic setting” with flowers, electric candles and a couch. While not all of the results have been analyzed, Hill did find that the longer the couple’s relationship was, the greater their decline in cortisol levels.

And ladies, to keep that spark alive, you might want to try out a wetter kiss with your guy.

“There’s evidence that men like sloppier kisses with a more open mouth,” Fisher said. “That suggests to me that they are unconsciously attempting to transfer testosterone to trigger the sex drive to woman.”

Men also view kissing early on in a relationship as more important relative to women, and they also look at it as the first step towards copulation, Fisher said.

But be careful, because a kiss can be a deal breaker.

A 2007 study at the University of Albany showed that 66 percent of women and 59 percent of men reported being romantically interested in a person, but after the first kiss those feelings of attraction ended, Fisher said.

“The first kiss was the kiss of death,” she said.

For couples who get beyond that initial kiss, though, their lip locking may stimulate any or all of the brain systems related to mating and reproduction.

Based on brain scans of 49 people who reported they were madly in love, Fisher proposed that humans have evolved three brain systems of mating and reproduction: sex drive, which motivates individuals to seek a variety of partners; romantic love, which pushes them to direct their mating energy on one person; and attachment, which allows them to sustain a bond long enough to raise a child.

Kissing therefore plays a key role in mate selection, one of the most significant things you’ll do in your lifetime, she said.

“Kissing is just the tip of the iceberg,” Fisher said. “I think we’re going to find all kinds of other chemical systems are in play in courtship that we are unaware of.”