[Cet article est issu du supplément Courrier ados, proposé avec le numéro 1780-81-82 de Courrier international en vente du 19 décembre 2024 au 8 janvier 2025.]
From 10 to 100 million bacteria, harmless in the vast majority of cases, are exchanged during a ten-second tongue kiss. But also 9 milliliters of water, the content of a teaspoon.
Kissing when you are in love is indeed sharing much more than feelings. There is a dedicated scientific field: philamatology. This discipline tries to understand why humans kiss and what are the upheavals that occur in their bodies when their lips touch.
“A positive effect on the whole body”
Thuy Do, who specializes in oral health at the University of Leeds in the United Kingdom, tells the German wave what “Microbial balance is essential for a healthy mouth, and that kissing could play an essential role in maintaining this balance, as it allows us to exchange microbes with our partners”. Quoted by the German public media, the microbiologist continues: “The mouth is the entry point to the body, it is connected to the intestinal microbiota and the skin. Kissing can have a positive effect on the whole body.”
Philamatologists describe in particular the effect of a kiss on the brain. It increases the level of oxytocin, nicknamed “love hormone”, according to an article published in 2023 by the Harvard Medical School. “We now know that oxytocin soothes stress and anxiety, and one study suggests that it could also have a positive effect on relaxation, confidence and psychological balance in general.”
A kiss also stirs comforting messenger molecules (neurotransmitters), such as endorphins, dopamine and serotonin. Kisses, hugs and other physical signs of affection also help reduce cortisol levels,“stress hormone”. Conversely, cortisol levels increase in cases of heartbreak or a breakup.
The future of the human species
A feeling of well-being and lightness invades the brain during a kiss, but the muscles are also extremely used. “Simple kisses require the movement of two muscles and burn only 2 to 3 calories,” calculated the editor-in-chief of the reference journal on medicine in the United States, theAmerican Journal of Medicine.
“In contrast, 23 to 43 facial muscles and 112 postural muscles [qui permettent au corps de se maintenir] are involved in a passionate kiss.” In this case, 5 to 26 calories per minute are consumed.
And that's not all. Something essential for the future of the human species also happens during a kiss. During the exchange of saliva, information about the body's defense system is also exchanged, which makes it possible to fight, for example, against microbes that enter our body. This would allow the woman to “judge whether the man would make an acceptable partner”, explained The Independent in 2012.
“The advantage is that if you bond with someone [avec un système de défense] different from ours, our children will be healthier and have a greater chance of survival,” indicated to the British newspaper Sheril Kirshenbaum, an American considered the queen of the science of kissing.
