There are a few things in life that couples don't share. They share houses, beds, the shower, their interests and even toothbrushes, which is why it is perhaps not surprising to find out that they also share bacteria.
It is not just one or two of these germs; we're talking about millions of bacteria shared by couples in a single kiss, or 80 million to be exact.
That is what researchers at the Netherlands Organization for Applied Scientific Research (TNO) found out when they set out the evolutionary purpose for kissing, a courtship act that is found in most major human cultures but nowhere else in the animal kingdom.
In a study whose results were published in the journal Microbiome, the researchers led by Professor Remco Kort of TNO's Microbiology and Systems Biology department recruited 21 couples strolling through Amsterdam's Artis Royal Zoo to conduct a "controlled kissing experiment" to find out exactly how many bacteria are swapped in a strictly-timed 10-second kiss, which they described as "involving full tongue contact and saliva exchange" or, in other words, a French kiss.
The researchers discovered that the microbiota of both partners were more similar to each other than that of strangers. They also found out that couples, who kissed more frequently, at least nine times every day, were more likely to have similar bacteria inside their mouths. The discovery was made after studying samples collected from each pair's tongues and saliva before and after the kiss.
The researchers also asked one person in each pair to drink a 50 ml cup of yogurt that contained strains of Lactobacillus and Bifidobacteria before sharing another kiss. After swabbing the tongue and saliva of the partner who did not drink the yogurt, Kort and his colleagues discovered that a single, 10-second kiss transfers, on average, 80 million bacteria from one partner's mouth to the other.
"There are a number of studies that show if the diversity in bacteria increases - more different types of species - this is a good thing," Kort tells Time. "If you look at it from this point of view, kissing is very healthy."
More than 7,000 kinds of bacteria live inside the mouth and trillions of microorganisms living in and on the human body comprise the microbiome, a collection of bacteria that helps strengthen the immune system, ward off diseases and break down nutrients for distribution to the different parts of the body.
Although Kort acknowledges that no scientific studies have yet been done on the effects of kissing on the body, he believes that kissing and kissing more often is beneficial to couples' health, as exposure to more types of bacteria prepares their bodies to better deal with infections and diseases.
So pucker up, ladies and (patho)gents!
