It is a moment of high anxiety in any romantic relationship. But now researchers have found that the first kiss may be even more important than anyone suspected.

While a kiss may just be a kiss for a man, for a woman it’s an all-important means of gauging a prospective partner’s compatability. She uses it, the study suggests, to assess a “rich and complex exchange” of romantic and chemical clues that pass between partners as their lips touch.

A “good kiss” will help convince her that the partner is worth perservering with but a man who is judged to be a bad kisser is unlikely to find himself invited in for coffee.

In the longer term the woman treats kissing as a means to induce bonding and to help her assess whether her partner has remained faithful and interested.

For men the kiss is much less important. It might be a source of hormonal information but it’s mostly regarded as a preliminary to sex. A man tends to regard a good kiss as one in which he’s allowed to use his tongue and is rewarded with moans of pleasure, the study found.

Dr Gordon Gallup, of the University at Albany in the United States, said: “The information conveyed by a kiss can have profound consequences for romantic relationships, and can even be a major factor in ending one.

“While many forces lead two people to connect romantically, the kiss - particularly the first one - can be a deal-breaker.”

The study, published in the online journal Evolutionary Psychology, suggests that clues to a person’s health are passed on by kissing.

These clues are picked up and understood - consciously or unconsciousy - by the kissers but are more important to the female, the researchers said, because she is more interested in a long-term relationship compared with the man who is often an “opportunistic mater”.

Women were more likely than men to take into account the smell of their partner’s breath, the taste of their mouth and the state of their teeth during a kiss.

“Females place a greater emphasis on kissing for making mate assessments,” the researchers reported. “Our data shows that females are more likely to base evaluations of their partner’s kissing ability on chemical clues, ie, the breath and taste.

“This study provides evidence that romantic kissing may have evolved as an adaptive courtship strategy that functions as a mate-assessment technique, a means of initiating sexual arousal and receptivity, and a way of maintaining a bonded relationship.”

Women were less than half as likely to have sex with a man without first enjoying a kiss, and the study also found they were less likely to tolerate the use of tongues on a first date.

By contrast, men showed themselves to be far less fussy and were much more likely both to continue to want sex even with a bad kisser or without bothering with a kiss.

Once a relationship was established, the researchers found, men grew less interested in kissing whereas women continued to give kisses a high priority. They were much more likely to kiss a partner after sex than men were.

Researchers made their findings after analysing three surveys of a total of 1,041 college students, most of them aged 18 to 25.

The study was conducted by academics from the University at Albany, the City University of New York and Albright College, all in the United States.

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