By Brittany Dingler
While the approaching of Valentine’s Day usually marks ubiquitous exchanges of chocolates, roses, and “punny" cards, most of us do not realize the other “something special” we are giving our significant others: bacteria. These invisible microbial guests outnumber our own cells ten-fold, as they enjoy a life of free meals, nice homes, and protection.
In our mouths alone, we harbor up to 200 species of bacteria, adding up to a whopping 1,000 to 100,000 microbes (Stevens & Desrocher, 1997). The bacterial cocktail within our mouths is usually unique to us and largely depends on our oral hygiene habits, diet, genetics, and overall health. However, a study carried out by Kort et al. (2014) found that a few distinct species can enjoy shared custody between individuals in a relationship. Here, the researchers discovered that hours after consuming a probiotic yogurt, those who engaged in “intimate kissing” shared Lactobacillus and Bifidobacterium bacteria. Perhaps less romantic is their finding that, on average, a 10-second kiss facilitated the transfer of 80 million bacteria.
Though this might seem gross enough to make you temporarily swear off intimacy and keep your chocolate box to yourself, it is worth considering the evolutionary benefits to why this particular act of intimacy is important to us as humans. Kort et al. (2014) have evidence that, although we are not the only animals who kiss, our particular form of saliva-swapping smooching may have enabled our ancestors to do a quick, necessary profile of the dietary and metabolic fitness of our potential mates via implicit “chemical cues.” This is not entirely unlike our innate propensity to favor those with symmetrical faces and silky, shiny hair - qualities that also speak to the health of the individual. Additionally, the famous “cuddle hormone,” oxytocin, spikes during a kiss, which facilitates feelings of attachment, a key component of a species’ survival.
On a more appreciable level, humans’ naturally residing bacteria help to fight off of pathogenic (disease-causing) bacteria that could make us sick or create infection by outcompeting the ill-meaning microbes for space and nutrients. As a result, our immune systems may be benefiting from our intimate exchanges, while taking “what’s mine is yours” to a whole new level.