The Differences in Gender -- Sealed With a Kiss

Moreover, kissing is clearly a much bigger potential deal-breaker for women than for men. Women were much more likely to say they would refuse to have sex with a bad kisser.

"Women are definitely using kissing to make an assessment about the male. If he's a bad kisser, then she's not going to want to have sex with him. She's getting a lot of information from that kiss," she said.

Men were also more likely to expect kissing to lead to sex. Men assumed that would be the case about half the time; women only about one-third of the time. And it made no difference to men if they were in a short- or long-term relationship.

"Men tend to think kissing should lead to sex no matter what," Hughes said.

That fits with other research, said Beverly Palmer of California State University, that has found that men and women often interpret nonverbal cues differently.

"When the woman is first kissing the man, she's not necessarily sending the signal, 'Let's go to the next stage' -- but the man is reading it that way," Palmer said. "So both can get themselves into difficulties if they don't verbalize their true intentions."

Men were also much more likely to want to exchange more saliva during a kiss.

"Males like the very moist, wet open-mouth kisses," Hughes said. "We didn't expect that."

Men tend to have less acute senses of taste and smell than women, which could explain that finding, she said.

"Perhaps males need more saliva to make subtle mate assessments," she said, noting that previous research has suggested that a woman's breath changes across the menstrual cycle. "He may be subconsciously detecting whether she's fertile or not."

Fisher was intrigued that men also were more likely than women to think a kiss could end a fight. "I didn't expect that. Maybe it's because they know women find kissing more intimate, so they are doing something not for themselves but to win women over," Fisher said.

Another recent study that measured oxytocin levels of kissing couples found kissing only caused the bonding hormone to rise in men. But those researchers speculated that might have been because the experiment took place in the decidedly unromantic setting of a college health center.

"Our working hypothesis was males are less affected by the ambiance, if you will," said Wendy L. Hill of Lafayette College in Pennsylvania. The study did find that kissing lowered levels of the stress hormone cortisol in both sexes.

Women in Hughes's study were more likely to say kissing was important before, during and after sex, as well as throughout a relationship. "That supports the idea that females are using kissing to create a bond," Hughes said.

"No wonder we remember our first kiss," Fisher said. "No wonder we're nervous about our first kiss. We haven't known why. This helps explain it."