Lip Service: 10-Sec Kiss Shares 80mn Bacteria To Build Immune System, Scientists Say

Reuters / Christian Hartmann

A 10-second French kiss can transfer up to 80 million bacteria.

New scientific data give an evolutionary explanation to the act of kissing, which, in fact, is a way to strengthen the immune system and fight disease.

According to the Netherlands Organization for Applied Scientific Research (TNO) 80 million bacteria are transferred during a 10-second lip lock. And in order to share similar salivary microbiota, partners should kiss at least nine times per day.

Microbiota are a complex mix of over a hundred of trillions of microorganisms that humans carry. They are vital companions in fulfilling such tasks as digestion, nutrient synthesis and prevention of disease. The mouth, which provides bacteria with an ideal environment, hosts over 700 kinds of them.

"Intimate kissing involving full tongue contact and saliva exchange appears to be a courtship behavior unique to humans and is common in over 90 percent of known cultures," lead author Remco Kort said in the press-release.

“Interestingly, the current explanations for the function of intimate kissing in humans include an important role for the microbiota present in the oral cavity, although to our knowledge, the exact effects of intimate kissing on the oral microbiota have never been studied.

"We wanted to find out the extent to which partners share their oral microbiota, and it turns out, the more a couple kiss, the more similar they are," Kort added.

Dutch scientists have explored the microbiology behind the kissing with 21 couples aged 17 to 45 participating, including one female and one male homosexual couple, in a test that took place at the Artis Royal Zoo in Amsterdam. They published their figures in a study called ‘Shaping the oral microbiota through intimate kissing’ in the journal Microbiome on Monday.

During the experiment, participants had to kiss before and after they consumed a probiotic drink containing specific types of bacteria including Lactobacillus and Bifidobacteria, that are rarely found in the mouth.

Swab samples revealed that while tongue microbiota were more similar among partners than unrelated individuals, this similarity didn’t rise with more frequent kissing, unlike the case with saliva microbiota. 

A display of Petri dishes with microbes growing in them at Micropia, the world’s first "interactive microbe zoo" in Amsterdam (AFP Photo / Maarten Van Der Wal)

The psychology behind the kiss was not left aside, with about 74 percent of male participants in the questionnaires reporting higher intimate kiss frequencies than women of the same couple. It seems, a man’s 10 kisses per day equal just five reported by his female partner.

Scientists also noted the significance of shared lifestyle, environment, or genetic factors in the viability of long-term collective bacteria colonization.

The Dutch biologists worked in collaboration with the Amsterdam’s museum Micropia, the first museum dedicated to microbes in the world, which opened in September. It features a ‘Kiss-o-meter’, able to rate a kiss on a scale from a “dry, prudent kiss,” which transfers just 1,000 bacteria, to a “hot” one, exceeding millions. In the museum, the couples who shared a kiss were also provided with an instant analysis of the bacteria they exchanged.