A single kiss – 80 million bacteria

Scientists have demonstrated that a 10-second “intimate kiss” can transfer a whopping 80,000,000 bacteria from one mouth to another, according to a new report in the journal Microbiome.

A team of Dutch researchers recruited 21 couples who happened to be visiting the Artis Royal Zoo in Amsterdam. All 42 volunteers (whose ages ranged from 17 to 45) allowed the researchers to wipe their tongues with a cotton swab several times. They also agreed to spit into sterile tubes and answer questions about their kissing habits.

The researchers found that the particular community of bacteria living on a volunteer’s tongue was more similar to the bacteria on his or her kissing partner’s tongue than to a stranger’s tongue.

Some of the volunteers were given a probiotic yogurt drink spiked with a marker bacteria. Researchers swabbed their tongues and asked them to kiss their partners. Then the partners had their tongues swabbed. Comparing the contents of the swabs, the researchers calculated that a single kiss can deposit 80 million bacteria from one tongue to another.

And here’s a bonus finding: The men said they kissed their partners an average of 10 times a day, while the women recalled kissing only five times a day. The researchers concluded that the men were most likely exaggerating the frequency of their romantic encounters.