A kiss isn't just a kiss: It's also an opportunity to transfer millions of germs.
Read: Choice kissing tips
That's the word from new Dutch research that suggests 10 seconds of lip lock can translate into 80 million germs moving from one person to the other. And two people who smooch a bunch of times each day will end up sharing similar germs.
Behaviour unique to humans
"Intimate kissing, involving full tongue contact and saliva exchange, appears to be a courtship behaviour unique to humans and is common in over 90 percent of known cultures," study author Remco Kort, from TNO's Microbiology and Systems Biology department in the Netherlands, said in a BioMed Central news release.
Kort, an adviser to the Micropia museum of microbes in Amsterdam, added, "To our knowledge, the exact effects of intimate kissing on the oral microbiota [microscopic living organisms] have never been studied.
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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."
In one experiment, the researchers gave 21 couples a probiotic drink containing bacteria before they kissed.
Transfer of 80 million germs
Swab samples afterwards showed the transfer of those 80 million germs.
The researchers also found that tongue germs were more similar among couples compared to people who don't know each other.
Read: Rediscover the lost art of kissing
But in the big picture, according to the news release, mouth germs play only a small part: The mouth is home to more than 700 types of bacteria, but the body houses more than 100 trillion microorganisms, which help with tasks like fighting disease and digesting food.
The study was published in the journal Microbiome.
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