It's no surprise most people find kissing pleasurable, since there is a larger area of the brain devoted to sensations from the lips than from the entire torso. Not only that, but five of our 12 cranial nerves are activated during kissing.
"Kissing is an enormous stimulant to certain brain systems. A huge amount of biological information appears to be sent to your brain during a kiss. This may be why a kiss with a stranger immediately turns you on or off," says Dr Helen Fisher, a professor of anthropology at Rutgers University in the US and author of Anatomy of Love (Random House).
"Kissing may be an evolutionary mechanism. It seems women are more attracted to men who have opposing immune systems, which would provide the best protection for offspring."
In good news for Valentine's Day lovers, activating certain nerve endings through kissing also signals our brain to produce oxytocin, a hormone that promotes calmness and wellbeing.
Increased levels of oxytocin are also produced by massages, suggesting that kissing could also be a natural de-stressor.