CHICAGO (Reuters) - Valentine Lotharios beware: There's a lot riding on a kiss, new studies on the science of smooching suggest.
Researchers said kissing sets off a complex set of chemical reactions, and in some cases, a bad kiss could be the kiss of death for a burgeoning romance.
"A kiss is a mechanism for mate assessment," said Helen Fisher of Rutgers University in New Jersey, who is presenting her findings on Saturday at the American Association for the Advancement of Science meeting in Chicago.
Fisher, an anthropologist, told a news briefing that kissing is something more than 90 percent of human societies practice, but scientists are just beginning to understand the science of kissing, which is known as philematology.
One theory of kissing is that it is intended to promote bonding. Wendy Hill, a researcher at Lafayette College in Pennsylvania who is presenting her findings at the meeting, set out to test this on college students.
She was looking for changes specifically in oxytocin, a "love" hormone linked to feelings of sexual pleasure, bonding and maternal care. Since oxytocin has been known to lead to decreases in the stress hormone cortisol, she decided to look at that as well, she told reporters on Friday.
The researchers studied 15 heterosexual college couples between 18 to 22 who were assigned to either go off and kiss in a room in the college health center or just hold hands and talk to each other for 15 minutes.
Blood and saliva tests showed that men in the kissing group had a burst of oxytocin, but in women, levels of this hormone fell. "Cortisol levels for everyone declined," Hill said.
Curiously, she noticed that females using birth control pills had higher levels of oxytocin than those not taking the pills, which may been a factor in the findings in women.
Hill also said the atmosphere in the health clinic may have had something to do with the findings.
"We are exploring the possibility that the setting was not very romantic," she said. The next study will take place in a secluded room at the back of an academic building with flowers, candles, a sofa and jazz music playing in the background.
Fisher is taking a different approach in her research.
She has conducted a number of brain imaging studies and believes kissing can access any one of three primary brain systems used for mating and reproduction.
One is the sex drive, which is tied primarily with testosterone, she said. The second is romantic or passionate love, which she said motivates people to focus on one mate.
And the third is attachment, which helps couples stay together, at least long enough to rear a child.
Fisher said she thinks kissing activates different chemicals that stimulate these different regions of the brain.
"We do have evidence that saliva has testosterone in it. And there is also evidence that men like sloppier kisses, and more open-mouthed kisses. That suggests to me they are unconsciously trying to transfer testosterone to trigger the sex drive in women," said Fisher, who thinks kissing is just the tip of the iceberg.
"I think we will find all kinds of chemical systems are at play in courtship that we are not aware of," she said.
Editing by Vicki Allen