A couple kiss after a mass wedding in Manila. (AP)

Chicago, Feb. 14 (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 presented her findings today 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 per cent 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, 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.

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 centre 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.