Before you make out with your valentine this year, make sure you know what you are getting in to. According to a recent study, a kiss that lasts about 10 seconds can swap about 80 million microbes from your mouth to his or hers. (1)
In this study, twenty-one couples ages 17-45 had their mouth microbes evaluated before and after kissing. We are talking French kissing here, of course. To their surprise, the researchers found that couples had similar mouth bacteria even before they kiss. Basically, you are who you spend the most time with. Over time, we populate our homes with a certain stable of microbes that many family members will share.
Then, they gave one partner 50ml of a probiotic-rich yogurt and had them kiss their partner. The probiotics from the yogurt increased on the kissed partners tongue by 3.6 times after the yogurty kiss. The amount of probiotic from the yogurt in the saliva of the partner kissed increased a whopping 49 times. The researchers calculated this to be about 80 million microbes swapped per kiss.
The Evolution of a Kiss
It turns out that many animals, including fish, birds and primates, engage in some type of mouth-to-mouth contact, but only humans go all the way. In one survey, 90 percent of human cultures engage in intimate kissing with full tongue contact and saliva exchange. (1)
Researchers believe that such intimate kissing may have played a larger role in our evolution than partner assessment, bonding and mating. Mouth microbial diversity is a good thing, and kissing helps the process. While some of those microbes from a kiss only hang out for a few hours, others may become permanent residents, making the kiss a possible means of a microbial transplant for the oral microbiome.
I’m sure by now you have all read about the medical wonderment of a fecal transplant. Well, some researchers believe a mouth saliva transplant may be a viable way to transplant good bugs from one oral microbiome to another. Perhaps, if a child is prone to cavities, they could get an oral microbial transplant from another child who was cavity-free, theorized one researcher.
Researchers believe the act of a mother kissing her baby may have been a way to boost the immunity of their infant. Studies have shown that children who lack certain mouth microbes, like Streptococcus salivarius, are more susceptible to getting sick compared to children with a healthy population of microbes. (2,3) There are many other studies suggesting that when Streptococcus salivarius is re-populated in the mouth, immunity is boosted. (6,7,8) The mouth has over 700 species of microbes and diversity matters. Studies show that Americans have less microbial diversity than those in other cultures. Perhaps this is due to antibiotic use, an overly sterile environment – or just a national kissing deficiency. (4)
The Modern Day Kissing Booth
Maybe the Renaissance fair kissing booths were an evolutionary key that boosted immunity after the Middle Ages when we needed it the most. Today, you can go to the first Microbiome Museum in the world and kiss away while they check how many microbes you swapped. It is called the Kiss-O-Meter at Micropia in, where else, but Amsterdam. (5)