Let's continue dwelling on our Valentines theme. Many years after yours truly discovered the secret of a hot kiss, science has now also come up with an explanation. Wendy Hill, Professor of Psychology at Lafayette College, Pennsylvania found that a hot meeting of lips sparks a complex chemical surge into the brain that makes a lover feel excited, happy or relaxed. Also, it is being speculated that the hormone release may be triggered directly by an exchange of sexually stimulating pheromones in the saliva. “This study shows kissing is much more complex and causes hormonal changes and things we never thought occurred,” The Times quoted her. “We tend to think more about who we are kissing and how it feels, yet there are a lot of other things happening,” she added. Furthermore the study showed that while, for men, the process is triggered at the mere touch of lips, women need a little atmosphere thrown in to achieve the same chemical high. For women to experience the same high as men they need additional features such as a romantic environment, dimmed lights and mood music.

One puzzle is just how kissing might induce hormonal changes of the kind found by Professor Hill. There are clearly psychological factors involved but some researchers suspect saliva contains pheromones, chemical messengers known to be important in other mammals. In humans the role of pheromones is controversial because we lack organs to detect them. However, Sarah Woodley, an Assistant Professor at Duquesne University, Pittsburgh, believes that people can still detect them via the nose. Helen Fisher, Professor of Anthropology at Rutgers University, New Jersey, and author of Why We Love, believes that kissing produces not just a chemical, sexual thrill but can even improve overall health: “If you’re sharing your germs with somebody, you’re boosting your internal defence system.” Excuse me Professor, sharing germs good for your health? Ever heard about HIV/AIDS?

Anyway, no risk for HIV transmission through saliva, so let's keep on kissing and let the saliva exchange flow! Here is a quick reminder of why we engage in a practice that involves the exchange of, by one estimate, 278 colonies of bacteria per osculation. One theory is that kissing may have evolved as a means of unconsciously testing the fitness of a potential mate. On the grand scale, it could be a way of checking for genetic compatibility: Women subconsciously prefer the smell of men whose genes for a particular class of immune systems proteins are different from their own, presumably because offspring from such a match would have a stronger immune system, and hence a better chance of survival, than offspring from other men.

While there's no doubt that kissing helps us select mates - if a first kiss goes badly, there may be no saving the relationship - we also do it (especially those of us who have already selected our mates) because it feels good. Lips and tongues are packed with nerve endings. And then there's chemistry, which is where the new research by Professor Hill mentioned above comes in. So if you always thought you had a special chemistry with your loved one, you may finally have been proven right.