Kissing your man means revealing a lot more than just passion. US scientists claim that modern man lip locks to pick up traces of estrogen in a woman's saliva and thus gauge her fertility.
Anthropologist Helen Fisher of Rutgers University says that such behaviour may explain why men like wet kisses with more "tongue action".
While at a meeting of the American Association for the Advancement of Science in Chicago, Fisher said that wet kisses could also be an unconscious attempt to transfer testosterone to the woman, which would stimulate her sexual interest.
"Men see kissing early in a relationship directly as a step to copulation," she said.
According to Wendy Hill, a neuroscientist at Lafayette College in Easton, Pennsylvania, kissing may also serve as a way to assess the quality of a mate.
Fisher said that research has shown that the majority of men and women rate their first kiss as either "the kiss of death" or the blossoming of a new relationship.
The expert recently developed a personality test that measures four universal temperaments by using statistics from 40,000 people on the Internet dating site Chemistry.com.
Each temperament type was linked to activity levels of the brain chemicals dopamine/norepinephrine, serotonin, testosterone, and estrogen/oxytocin.
Fisher found that a person's temperament guides which type of mate they select-boosting her belief that love involves some very powerful brain chemistry.
"People sing for love; they dance for love; they write about love; live for, kill, and die for love," Fisher told National Geographic News.
"It's a wonderful addiction when [a relationship is] working well-but perfectly horrible when it's working poorly," she added.