Kissing is a universal sign of amorous affection. We wait for that first-kiss moment in romantic films, stumble through uncomfortable teenage make-out sessions and spy those PDA-friendly couples (you know the type). But have you ever thought about what kissing means beyond the obvious pleasures? Just how “germy” is a kiss -- and are those germs good or bad for us? (After all, mononucleosis is referred to as the “kissing disease" and most of us would likely prefer to avoid getting it.)
Since our bodies are made up of 10 times more bacteria than actual human cells, it’s no surprise that an act of physical intimacy such as kissing would result in a germy exchange. “Kissing really has a purpose, and in doing so, there is an exchange of microorganisms,” says Dr. Philip M. Tierno, Jr., Director of Clinical Microbiology and Immunology at the NYU Langone Medical Center. What this purpose may be however, is a matter of some contention.
Why Kiss?
According to a team of British scientists, kissing may be an important part of building up our immune systems -- specifically for women during pregnancy and childbirth. A 2009 study, led by medical researcher Dr. Colin Hendrie and published in the journal Medical Hypotheses, concluded that smooching was a key way for women to build up an immunity to cytomegalovirus -- a virus that can cause significant harm to a fetus in-utero (although it is harmless otherwise).
“Female innoculation with a specific male’s cytomegalovirus is most efficiently achieved through mouth-to-mouth contact and saliva exchange, particularly where the flow of saliva is from the male … to the female,” Hendrie told The Daily Mail. This also suggests that the longer a woman kisses the same person, the more likely she is to be immune to cytomegalovirus if she gets pregnant. So ladies, you may want to consider making out with your partner for at least six months before jumping to childbearing.
However, not everyone believes that germ-exchange was the primary, evolutionary driving force behind the practice of human kissing. Dr. Tierno has a different take. Although he concedes that the exchange of germs that occurs can be helpful to the human immune response, he says that this is simply a byproduct of kissing -- not the intention. Instead, he hypothesizes that kissing originated as a way for parents to feed their young. “Early humans, they knew nothing about the immune system, yet they were kissing,” he told The Huffington Post. “It originated by most authorities, from the direct mouth-to-mouth regurgitation of food.” This practice can still be seen in the animal kingdom -- the most obvious example that comes to mind is birds. And inevitably, if food is exchanged via the mouth, so are germs.
Good Germs Or Bad Germs?
Since we have such a plethora of bacteria residing both on and in our bodies (a recent study estimates that up to 500 different types of bacteria could be residing on our skin at any given point), it makes sense that most of the time this microbial flora is completely harmless. According to Dr. Tierno, only 1 percent of all known species of microbial flora are overtly pathogenic. The rest are quite innocuous. “For the main part of kissing, you do exchange flora,” says Tierno. “Sometimes it’s good, sometimes it’s bad [and] sometimes it means nothing.”
Where kissers should beware though, may seem pretty obvious. If your partner is visibly sick, you should probably take a break from physical intimacy. Although very few diseases are actually transmitted from what Tierno terms “deep kissing,” pathogens that cause conditions such as mono, strep throat and herpes can easily be exchanged orally. Additionally, if you or your partner have open sores or lesions in and on your mouths, kissing should absolutely be avoided. The one case of oral HIV-passage that Dr. Tierno could recall, occurred because both parties had gum disease.
And even though you may love them, just avoid kissing your pets altogether. “[Dogs] can carry worms, fungi and they can carry [pathogenic] pastuerella in their mouths,” says Tierno. “Although cats are worse.”
Beyond Kissing
Kissing is far from the only every day, intimate exchange that encourages the transmission of germs. What about shaking hands? Although 80 percent of all infectious disease is believed to be transmitted by direct and indirect contact, researchers at the Johns Hopkins Bloomberg School of Public Health, say that we need not worry too much about a friendly shake. The May 2011 study, published in the Journal of School Nursing, took samples from the hands of individuals before and after they crossed the stage at graduation ceremonies -- inevitably shaking a hand or two along the way. Once the samples were tested, the researchers found that only 7 percent of the samples contained pathogenic flora.
This doesn’t mean that we shouldn’t be diligent about washing our hands though. “Shaking hands can transmit some of the viruses that cause the common cold and diarrhea,” says Art Reingold, M.D., Professor of Epidemiology and Associate Dean for Research at UC Berkeley’s School of Public Health. “It can probably also transmit [the] hepatitis A virus [and] in the health care … setting, hands can spread Staph aureus and many other bacteria and viruses.”
So no need to be a germaphobe, but exercise a little common sense -- and some common cleanliness.