One 10-second kiss can transfer as many as 80 million bacteria, a study by Dutch scientists has found.
Published in the journal Microbiome, the study monitored the kissing behaviour of more than 20 couples. Scientists found those who kissed nine times a day were most likely to share salivary bugs.
Previous research suggests the mouth is home to more than 700 different types of bacteria. But the report revealed some are exchanged more easily than others.
The research team from the Netherlands Organisation for Applied Scientific Research (TNO) asked the couples a series of questions to assess their kissing habits; including how frequently they had kissed in the last year and when they last locked lips.
Scientists then took bacterial samples from the volunteers’ tongues and saliva before and after a strictly timed 10-second kiss.
One member of the couple then drank a probiotic drink, containing a mixture of bugs.
With the couple’s second kiss, scientists were able to detect the volume of bacteria transferred to the other partner. Whilst the bacteria in the saliva seemed to change quickly in response to a kiss, bug populations on the tongue remained stable.
“French kissing is a great example of exposure to a gigantic number of bacteria in a short time,” said Professor Remco Kort, who led the research.
“But only some bacteria transferred from a kiss seemed to take hold on the tongue.”
“Further research should look at the properties of the bacteria and the tongue that contribute to this sticking power.”
“These types of investigations may help us design future bacterial therapies and help people with troublesome bacterial problems.”