Jayney's Blog

The chemistry of a kiss

If you always thought you had a special chemistry with your loved one, you may finally have been proved right.

Throughout history, kissing has held different significance to different cultures – in ancient Greece, it was believed that kissing unleashed the soul upon a lover, while the Romans kissed their wives to gauge whether they were sober. More recently, scientists have discovered that kissing affects the “love chemicals” in the body.

Mutual caressing of lips and the exchange of saliva affects the levels of oxytocin – the “bonding hormone” – released into the bloodstream. Oxytocin is also released during childbirth, and is thought to aid the bonding of the mother and her newborn baby.

During kissing, oxytocin decreases in women while increasing in male partners. Researchers are unsure of why this difference exists, but believe it may be connected to women having naturally higher levels of oxytocin in their bloodstream.

As well as the effect on oxytocin levels, a 15 minute bout of kissing with a loved one has also been found to significantly lower cortisol levels – cortisol is also known as the stress hormone.

“The science of kissing, known as philematology, is an under-researched area of study,” said Wendy Hill, a professor of neuroscience at Lafayette College, Pennsylvania. Professor Hill carried out the experiments with the help of 15 heterosexual couple volunteers.

“Kissing is defined as a behaviour in which an adult male and female touch lips and engage in open mouth-to-mouth contact as a sign of greeting and affection. [It has been] proposed that kissing originated as an oral food exchange between mothers and infants, a behaviour known as pre-mastication,” Professor Hill said.

“Pre-mastication is still common among some non-western societies. This behaviour closely resembles the kiss that is shared between adult pairs since both involve positive oral contact, neural stimulation and saliva exchange,” she told the American Association for the Advancement of Science in Chicago.

Helen Fisher, an anthropologist at Rutgers University, New Jersey, added that kissing may also stimulate one of three primary brain systems that are involved in mating and reproduction – these are the sex drive, romantic love, and long-term attachment.

“The sex drive motivates you to seek a range of partners, romantic love motivates you to focus your mating energy on one individual at a time, feelings of attachment motivate you to sustain a pair bond at least long enough to rear a single child through infancy together,” Dr Fisher said.

She also added that kissing could have evolved as a biological strategy to assess a potential mate and initiate a sexual partnership.

“Men like sloppier kisses with more open mouths and more tongue movement. The hypothesis is they’re trying to get small traces of oestrogen to see where the woman is in her menstrual cycle to indicate the state of her fertility,” Dr Fisher said. “There are others who think that women use smell as they are kissing to deduce some things about the man’s immune system. That’s not proven yet.

“There’s some who suggest that by kissing a man a woman is unconsciously able to detect aspects of a particular complex of genes in the immune system, and that what they’re doing is being turned on by someone with different variations in the system,” she said.

By kissing, “you can the smell the health of their teeth and what they have been eating and drinking and smoking, and these are all devices we use to size up an individual before we do something like have sex with them,” Dr Fisher said.

“This is the tip of the iceberg. We are going to find many other mechanisms we unconsciously use to size up a person’s biological traits.”


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