Here's Exactly How Many Bacteria You Get From Kissing

Illustrated by Ly Ngo.
We've already seen pretty far inside a kiss, and new research takes us even farther in — to the bacterial level. It turns out there are a lot more living things involved in your makeouts than you might expect.
In the study, published this week in the journal Microbiome, researchers looked at the bacteria present in the mouths of 21 couples before and after they smooched. Specifically, they took samples from the tongue and saliva of each participant. The participants also completed a survey about their kissing habits (including frequency of kissing and length of average makeout session). The research showed that those who kissed the most frequently had the most similarities in mouth microbiota.
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And, in another part of the experiment, one half of each couple was given a probiotic drink. Then, the couple kissed and the other partner's mouth was swabbed. From this, the researchers were able to tell how many bacteria are transferred from one mouth to another in each sloppy, 10-second smooch. The answer was a staggering 80 million.
Earlier this year, other research looked at the amount of bacteria that are transmitted through different types of hand-based greetings. This small study, published in the American Journal of Infection Control, compared the number of bacteria that change hands during the traditional handshake, the fist bump, and the high-five. Their results showed that the handshake caused the most to transfer, followed by the high-five. But, the fist bump was the "cleanest" — meaning the fewest bacteria went from one hand to the other.
However, these bacteria aren't necessarily dangerous in any way. Many of them, including those found in our mouths, are completely harmless and even perform vital health functions that we wouldn't otherwise be able to do. So, it might be time for us to realize that if we're going to be interacting with other people, we're also going to be interacting with their (mostly harmless) little microbiota friends. These bacteria are not only necessary, but also pretty much inescapable.
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