AMSTERDAM -- Scientists in the Netherlands say new research shows couples who French kiss share millions of bacteria - and the more often they kiss, the more similar their saliva becomes.
The study, published the American scientific journal Microbiome, looked at 21 couples and measured how many microbes they exchange.
"In a single kiss of ten seconds, 80 million bacteria are transferred - on average - from one person to the other," says Remco Kort, principal scientist with Netherlands Organisation for Applied Scientific Research who collaborated with Amsterdam's Micropia Museum for the study. The museum claims to be the first dedicated to the science of microbes.
Study scientists asked one partner to drink a yogurt solution that contained bacteria not usually found in the mouth, then had the couples kiss for ten seconds.
"That allowed us to make an estimate of how many bacteria were transferred from one person to another," Kort says.
The researchers took samples from the tongue and saliva of the couples before and after they kissed. The study found that in addition to French-kissing couples' saliva appearing to seem the same, the bacteria on the tongues of the couples become more similar compared to samples from random people. The study conclusions cite other factors, such as couples sharing the same diet or toothpaste, that can affect the bacteria composition. Kort says a significant difference in height between French-kissing partners can result in a greater exchange of saliva - downward - to the shorter participant.
According to the Micropia Museum, the mouth hosts more than 700 kinds of bacteria. Researchers say the germs are normal and part of a healthy bacteria mix that lives in the human mouth, helps the body function and can help protect it from disease.
To help make the science more accessible to the public, Micropia assembled a "Kiss-o-Meter" - a machine and multimedia display that records people kissing. Depending on how long the couples kiss on camera, the display rates the affectionate act from an average 80 million bacteria-and-above exchange as a "steamy kiss," down to quick smooch registering only about 1,000 bacteria transferred as "prude."
Dutch couple Simon Ven Laarhoven and Floor Strijbis tried the Kiss-o-Meter during CBS News' visit to Micropia. They rate each other's French kissing skills as a "perfect ten." The Kiss-o-Meter wasn't as kind accessing their short-and-sweet peck:
"[Our kiss registered] only a thousand bacteria exchanged," Ven Laarhoven said.
"It called us a 'prude' - it said our kiss was a prude kiss," said Strijbis, laughing.
"I do know that that the mouth is one of the most bacteria-loaded places of the body, so 1,000 isn't that much," Ven Laarhoven, a doctor, said.
Micropia Museum Director Haig Balian says he set up the Kiss-o-Meter to show his teenage children what happens during a French kiss. He also says the display is great for couples on a date.
"When you go [to the museum] with someone whom you'd really like to kiss... you come up to the Kiss-o-Meter - and you can do it," Balian said with a smile.
Follow Alphonso Van Marsh on Twitter: @AlphonsoVM