A kiss is just a kiss...

Or so Louis Armstrong will have us believe. But as it turns out, a kiss is so much more than than that. It's actually an exchange of somewhere around 80 million different types of bacteria. Grossed out? But wait, there's more.

A new study published in the journal Microbiome has taken a closer look at what happens during a smooch. Specifically, researchers wanted to found out exactly how many bacteria are exchanged between partners with each kiss, and the number might surprise even the most dedicated kissers.

Studies suggest the mouth is home to more than 700 different types of bacteria, and this new research reveals that some are exchanged more easily than others.

For the study, researchers recruited 21 couples, ages 17 to 45 whose task it was to make out for science. Before their kisses, each partner had their mouths swabbed and spit tested to determine the type and number of bacteria present. Surprisingly, even before they smooched, most partner sets had similar bacteria profiles in their mouths. Researchers noted this could indicate a couple kisses frequently or it could be explained by more mundane reasons such as toothpaste or cigarette sharing. 

The couples were then swabbed and tested again after a passionate 10-second smooch and then again following another kiss after one partner drank a probiotic yogurt beverage. 

The researchers focused on two specific types of bacteria, Lactobacillus and Bifidobacteria, which together usually make up only about 0.15 percent of the bacteria in human saliva and 0.01 percent of the bacteria on the tongue.

Researchers were able to detect the volume of bacteria transferred to the other partner — on average 80 million bacteria in a single 10-second kiss.

The study was coordinated with the Dutch museum Microbia, where partners can step up to the Kiss-O-Meter for an instant analysis of the bacteria exchanged during each kiss. Researchers are hoping that by getting a better understanding of the bacteria profile of a kiss, they can learn how these ... um, bacterial transplants ... can be used to promote the spread of healthy bacteria and prevent future disease.

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One kiss = 80 million bacteria
New research puts a big number on the amount of bacteria swapped with each smooch.