It was love at first kiss for Honolulu real-estate agent Carol Sartain.

She and Jason Kage ended their first date at her front door with a passionate one.

"After our first kiss, I knew that I wanted to marry him," recalled Sartain, 36.

Now, four years into their relationship, the couple plan to tie the knot in March.

Kissing is so common that many of us don't think there's more to it than meets the lips. Kissing is a universal language — a cross-cultural phenomenon, a sign of love, affection and kindness. But it could also be nature's way of filtering certain people from our lives.

For example: Have you ever thought about why you liked someone until you kissed them?

According to research conducted by Gordon Gallup, a professor of psychology at the State University of New York at Albany, kissing is a way to weed out people who are genetically incompatible with you.

"The evidence suggests that kissing evolved as a mateassessment technique and that females, in particular, not only use kissing as a mate-assessment technique, but once they're in a committed relationship with a male, they continue to use kissing as a way to monitor and update the status of their relationship," he said.

KISS OF DEATH

Maybe that's why a kiss can spell the kiss of death to a budding relationship.

For Sartain, it never mattered how nice, handsome or rich a suitor was.

"I really am a firm believer that it's all about the kiss," she said. "By the first kiss, you could actually tell if you're going on more dates with that guy or if that's it."

In the same study, most of the respondents admitted that they were attracted to someone only to have that attraction wane after they kissed him or her for the first time. After a bad kiss, they were no longer interested in building anything solid with that person.

"There may be unconscious mechanisms that would make people make an assessment of genetic compatibility through a kiss," Gallup said.

Shellie Paiva, of Royal Kunia, remembers a horrible first kiss when she was in high school.

She was at a football game with her "steady" when he leaned over to plant one on her.

"There was slobber everywhere, and it was disgusting," said the 35-year-old police officer. ... "I thought, 'No, I can't do that anymore.' "

Paiva, who is now married, described her first kiss with husband Moku as "the best kiss." "With Moku, it's like (I never) want to stop, and it's always been like that from the very beginning."

Danielle Smith of Satellite Beach, Fla., recalls a similar experience with a bad kisser.

"It was like, what the heck was that?" she said of the sloppy, wet kiss. "It was horrible."

Now engaged, Smith said she got "butterflies" after her first kiss with her fiance.

"It was exciting, like, 'Oh, gosh,' " she said. "Kind of like where you feel like you're in high school again, just kind of giggly."

MEN VS. WOMEN

Gallup's study, which involved about 1,000 college students, also suggests that men and women kiss for different reasons.

According to Gallup, men tend to kiss to gain sexual favors or to reconcile, whereas women kiss to check the status of their relationships. Kissing is also a way for men to connect with their partners and keep them interested physically.

While the male respondents in the survey say that they would be more than happy to get physical with women who were bad kissers, most of the female respondents said they wouldn't dare.

This finding may be biologically significant as well.

According to Gallup, women have a small reproductive window in their lives, which can be why women tend to place so much more emphasis on that first kiss. Biologically, women don't have the time, nor can they afford to get it wrong.

INFORMATION SWAP

Smith, the Satellite Beach, Fla., fiancee, said she continues to kiss a lot during her relationship — but that lustful kiss has worn off and has been replaced by a more typical kiss as the status of her relationship has progressed.

"Once you get to that kind of comfort level, it's not as much," she said. "More so now, it's a hello, goodbye type thing."

Gallup's research says that while a kiss won't necessarily make a relationship, it can kill one.

"There's an incredible amount of exchange of information, even the exchange of chemical information (during a kiss)," he said.

That first-kiss bug can strike men as well. Scott Burkett said that his first with his partner and fiancee Dawn Falotico was "magical."

"It was in her bird's room, and it's painted blue and has stars on the ceiling that glow when you turn the lights off," said Burkett, who also lives in Florida. "It was perfect."

The two, who've known each other since 1979, lost touch and reconnected again. They are engaged to be married in January and couldn't be happier.