MELISSA BLOCK, HOST:
A kiss, it turns out, is not always just a kiss. At least, that's what some new research suggests. NPR's Rob Stein reports that kissing apparently can influence the kinds of microbes that inhabit our mouths.
ROB STEIN, BYLINE: There are trillions of microorganisms living all over the human body and these microbes may play important roles in our health so Remco Kort, a microbiologist in the Netherlands, wanted to see what kissing does to the bacteria in our mouths.
REMCO KORT: Kissing is really an example of exposure to a large amount of bacteria and it's such typical human behavior so I was very curious to see as a microbiologist how many bacteria are actually exchanged during a kiss.
STEIN: Kort and his colleagues studied 21 couples. They asked one partner to drink yogurt made with bacteria that's not usually found in the mouth and then kiss their partner to see how many organisms get transferred in a single smooch and what they found surprised them - making out for 10 seconds can transfer 80 million bacteria.
KORT: Depending on the type of kiss you will have a different readout. With a very, let's say, modest kiss only a relatively small number of 1,000 bacteria are exchanged, but in the case of a wet kiss - intimate kiss - then we come to this number of 80 million.
STEIN: The researchers also grilled the couples about kissing, like how they kissed and how often they kissed and checked out the microbes that were permanently living in their mouths. In the journal Microbiome the researchers report what they found. The microbes in the mouths of couples are much more similar than those in the mouths of strangers.
KORT: To our surprise, we found that those people that are intimately related - so partners - they share much more of their bacteria on their tongue and then unrelated individuals. That's really important of the study.
STEIN: Kort was surprised because scientists had thought our microbes pretty much got set in the first few years of life and usually didn't change much after that, but Kort's study says who you kiss can clearly switch things up, especially if you kiss them a lot.
KORT: If you have a frequency of more than nine times per day then the collection of bacteria is more similar.
STEIN: Other scientists say the findings are interesting because the microbes in our mouths seemed pretty important. Floyd Dewhirst studies mouth microbes at Harvard.
FLOYD DEWHIRST: The organisms in the mouth surprisingly can indicate a lot about health, you know, elsewhere in the body by what kind of things are secreted into the saliva to help the organisms grow so that the mouth truly does reflect what's going on elsewhere in the body.
STEIN: The new research is just the latest discovery about kissing, according to Sheril Kirshenbaum, the author of "The Science Of Kissing."
She says kissing does way more than just show affection.
SHERIL KIRSHENBAUM: This is just one more example of how science is only barely scratching the surface of the significance of kissing and what it really means. A kiss is not just a kiss. There's a lot more beneath the surface.
(SOUNDBITE OF SONG, "AS TIME GOES BY")
STEIN: So all this raises another question, is a sigh just a sigh?
Rob Stein, NPR News.
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