The Science of Kissing: What Our Lips Are Telling Us

by Sheril Kirshenbaum

  1. OUR KISSING COUSINS

  Chapter 2 journeyed around the animal kingdom for a colorful sampling of kissing-like behaviors in our close and distant relatives. The species whose kisses seemed the most similar to our own was an amorous primate cousin, the bonobo, whose pink lips and dexterous tongue can be used to express all manner of affectionate social behaviors. Since the study of the relationship between hormones and kissing in humans has proven difficult—apparently due to the stresses of an unnaturally clinical testing environment—it’s possible that research on bonobos may shed new light on our outstanding questions.

  To find out, anthropologists and endocrinologists might collaborate, starting from the foundation laid down by Wendy Hill and Carey Wilson of Lafayette College. As discussed in chapter 8, their team used saliva and blood samples to measure oxytocin and cortisol levels in couples before and after kissing sessions, with the expectation that kissing would decrease stress and increase the flow of hormones associated with emotional attachment. To remove the influence of experimental anxiety, a similar study could be undertaken in bonobos under natural conditions. As a result, scientists might develop a more complete understanding of the role of kissing in their social interactions—and by extension, greater insight into our own.

  How could the study work? Scientists already working with sanctuary bonobos would have to gather hormone samples from subjects well accustomed to frequent kissing sessions in that setting. Certainly they would not feel as uncomfortable or as anxious as the Lafayette College students, and therefore data should be more reliable. The methodology for obtaining it is not difficult: In the past few years, hormone tests have been conducted on bonobos’ saliva by giving them cotton swabs coated in powdered SweeTarts. Once the sugar is gone and the cotton discarded, swabs are collected and analyzed. So theoretically this procedure could be combined with simple blood tests to measure oxytocin and cortisol levels before and after a pair is observed to tongue-kiss. If scientists were to record a rise in oxytocin and a drop in cortisol, it might demonstrate the importance of kissing for developing and maintaining social bonds in a closely related species. This would provide greater evidence that humans and bonobos kiss for similar reasons and possibly suggest that kissing’s true nature may be even more universal than we currently acknowledge.

  2. NO ASSEMBLY REQUIRED

  The simple action of tilting our head prior to kissing can actually offer some valuable clues about nonverbal communication between people. University of Chicago psychologist Howard Nusbaum suggests that conducting a study that recruits volunteers to kiss in the lab might allow social scientists to observe how this phenomenon works. If strangers bump heads more frequently than couples in established relationships, scientists might conclude that experience matters. However, research on other gestures has demonstrated the way that humans are extremely good at picking up on instantaneous nonverbal cues. So familiarity with a kissing companion may not be particularly important.

  In addition, some participants could be required to remember a series of numbers (this is known as a “cognitive load”) to determine if a mental task results in a higher collision rate, since concentration shifts. Finally, one person in an established couple might be instructed to initiate a kiss in the opposite than normal direction to find out whether a partner can easily accommodate the switch.

  Although head tilt may seem perfunctory, it may be useful to help scientists explore the significance of the way we interpret simple social cues from others and how that informs our actions.

  3. THE CONTEXT OF KISSING

  While it would be extremely difficult, if not impossible, for two people to kiss in a brain scanner, we may yet be able to use brain imaging technology to learn more about the neuroscience of kissing; namely, how the context in which a kiss occurs influences the overall experience.

  In chapter 5, we saw that during a kiss, many cues are transmitted that help our brains and bodies figure out what to do and influence the neurotransmitters regulating how we feel and behave. All the many and varied elements that make up the environment in which a kiss occurs—mood, ambiance, strength of the connection between two people—thus play a critical role in the outcome of any exchange. At the most basic level, the recipient has to interpret the origins of the kiss—including whether it is delivered from a friend, lover, or enemy. This information then influences the way he or she reacts. And while the methodology to study this process may not be simple, it is probably possible by using an fMRI machine.

  Previous research on pain response has demonstrated that the presence of a loved one can reduce the severity of discomfort. In a 2006 study, for instance, sixteen married women were put in an fMRI machine knowing they would feel an electric shock on their ankle while holding the hand of either their husband, an anonymous male experimenter, or neither. This was the first experiment documenting the way that touch can affect brain response to a threatening situation. Happily married women reporting the highest levels of relationship satisfaction and holding the hands of their husbands experienced the least discomfort during the experiment. In other words, knowledge about who is present in the environment interacts with a person’s physiology to determine how he or she ultimately experiences a situation. This relates to why, when it comes to kissing, the identity of the other person has a strong influence on how we feel.

  Once again, there’s a technological constraint here—we cannot fit two heads in an fMRI scanner. However, hand-kissing might serve as a workable alternative to investigate how our response to a kiss varies based on the person who delivers it. As we observed in chapter 3, hand-kissing has been recorded since antiquity. So using a methodology modeled after the fMRI hand-holding experiment described above, a similar study could investigate how the kissing experience is influenced by the kisser’s identity. Like the women in the previous experiment, subjects in the fMRI machine would be told who is kissing their hand (a spouse or a stranger). By monitoring brain activity, scientists would then be able to observe how the response varies depending upon the relationship between the subject in the machine and kisser. If different responses are noted after repeated trials among many test subjects, this kind of investigation may finally be able to show that a kiss is not “just a kiss,” but rather highly dependent on the context in which it occurs.

  4. THE TEST OF TIME

  Another intriguing area would be to examine attitudes on kissing over time in relationships. After all, the bond between two people can transform tremendously as partners undergo significant life changes. Some couples grow together over time, others apart. By learning about the role of kissing as relationships and their participants mature, we might be able to provide couples with better guidance, especially for keeping a marriage together and understanding the physical and emotional needs of another person at different stages of life.

  To find answers to these types of questions, scientists could conduct what’s called a longitudinal study—one that follows the same individuals over a long time. They could ask men and women questions about their kissing preferences very similar to the ones asked in the Albany social survey described in chapter 6: what appeals to them in a kiss, what they notice most about a kissing partner, how significant they consider kissing to be in their committed relationships, sexual encounters, and so on. By continuing to survey the same subjects at five-year intervals, we might start to observe trends in how perspectives on kissing change over time. The interviews might begin when the subjects are college-aged, but the continual stream of data would ultimately cast light on the preferences of both genders as we age.

  Longitudinal research in other closely related areas suggests that in such a study, scientists might find distinct differences. For example, would the value one places on kissing frequency and intensity decrease for men and women as family responsibilities generally pile up toward middle age? By eighty, might participants find amusement looking back at what motivated them to kiss another person in their twenties?

  On a re
lated note—and while this might be scientifically challenging—it would be highly illuminating to obtain hormonal data on the very same subjects, so as to observe how the bodies of each participant changes alongside his or her responses. After all, relationships ebb and flow along with physical intimacy. Perhaps we would see that changes in kissing preferences are associated with increased or decreased testosterone and estrogen levels, or observe women’s attitudes notably shifting post-menopause. This kind of investigation could provide insight into the influence of the aging process on how we foster important social bonds with loved ones and teach scientists more about what may be involved in the success of a long-term commitment.

  Of course, while such data are certainly not unobtainable, we would inevitably have to wait a very long time—and depend on a very committed team of researchers—in order to learn from them. But it would be interesting to test whether kissing between two people in a decades-long happy marriage promotes higher oxytocin levels than kissing between members of a young couple early on in their relationship. These studies could be tweaked to consider multiple theories about kissing, stress, and attachment.

  The results really matter when you consider the longevity of relationships. Most of us hope to make a lifelong commitment at the altar, but divorce statistics around the world demonstrate that unfortunately, many are unable to follow through. If research is able to demonstrate that physical intimacy—measured by factors such as the frequency of kissing—is correlated with increased relationship satisfaction, then it’s possible some type of “kissing therapy” might even be incorporated into marriage counseling.

  5. FOLLOW YOUR NOSE

  Olfaction provides yet another area where kissing related research has miles to go. As highlighted in chapter 7, scientists already have much evidence suggesting that our sense of smell plays a large role in our decision to venture into a romantic relationship. It may even provide a means of assessing another partner’s genes, and particularly his or her major histocompatibility complex, or MHC.

  But the MHC is only one part of our very vast human genome. The real relationship between our sense of smell, our genes, and compatibility is likely far more complex and involves many other regions. As geneticists learn more about the roles of different human genes in the coming years, they may also find a firmer physiological basis for understanding how our scent preferences play a role in choosing a partner, and why or if such choices matter down the line, when children come along.

  6. DIVERSITY MATTERS

  When the methods of hormonal experimentation are refined, it would be interesting to study subjects from various age groups and a diversity of backgrounds, clarifying whether their results might apply to a larger demographic than the limited sample studied at one university.

  In chapter 6, we learned that heterosexual men and women express different preferences about kissing style. This likely relates both to hormones and to cultural expectations, so it would be very illuminating to look more closely at how a person’s sexual orientation may play a role in his or her attitudes toward kissing. Consider perhaps a large social survey, similar in style to the one given at the University at Albany, but including members of every community—lesbian, gay, heterosexual, bisexual, and transgender.

  Likewise, we have seen how kissing customs and styles vary tremendously around the world. The same survey may therefore yield distinct results in different countries. For example, would men in Brazil, India, and China report the same preference for tongue-kissing that American men seem to enjoy? Would teeth be as significant to women in Australia, Japan, and Spain? Despite physiological similarities, I strongly suspect that culture would influence the results, but this has not yet been tested scientifically.

  WHO CAN SAY WHERE kissing research will go from here? If you were to map out the course of scientific progress for any discipline, the resulting diagram would look like a branching tree. Some limbs would break or die off as studies hit roadblocks or as the scientific community lost interest. Meanwhile, other limbs would continue to grow in all sorts of unpredictable directions, as science bursts forth to accommodate emerging ideas.

  With this image in mind, my hope is that I have highlighted some of the outstanding questions, and so may inspire new research avenues for others to pursue, particularly in neuroscience. After all, while kissing hasn’t been fully ignored by modern scientific investigators, it also hasn’t received very much attention. Perhaps we’re beginning to see that change.

  CHAPTER 12

  The Future of Kissing

  The kiss’s popularity and appeal has changed throughout history, often as a result of shifting social mores and cultural norms. Just as nineteenth-century explorers brought the behavior to people around the world, television and film expanded its exposure in the twentieth century. Today, the human population is moving and networking faster than ever before, and kissing customs and opportunities continue to be in a state of flux thanks to emerging technologies. So we’ll now examine how kissing may be changing in the twenty-first century as we glimpse into the future.

  The research I’ve highlighted emphasizes the significance of kissing in relationships, so it’s worth considering how the dating landscape is changing in our increasingly wired society. Many people are looking to the Web in search of partners through sites like Match.com, eHarmony.com, and others. And no wonder: It’s fast, efficient, and the singles pool seems virtually limitless.

  Online daters get to know each other’s “personalities” via their profiles long before they venture into close proximity. On the surface, it may seem like a great way to weed out bad matches while retaining a very large selection of potential partners to choose from. Yet there are also some notable drawbacks that should be obvious at this point in the book. Although the Internet is a wonderful innovation, it does not provide the opportunity to sample the scent, taste, and other nonverbal cues emanating from those across the screen. These naturally important signals are entirely absent from a digital “wink,” “poke,” “flirt,” or whatever means is used to initiate the first communication. As a result, it forces us to make decisions without the instincts that have evolved to guide us best. Dates are selected without visual, tactile, and other clues guiding users. So in a sense, when we’re dating online, we’re flying blind—or at least handicapped—due to such limited information compared to an in-person encounter.

  On top of that, the factors that traditionally spark our interest in someone are likely less obvious on the Internet, as greater emphasis is placed on superficial attributes or a carefully worded profile. Research on online dating trends has revealed that a person’s apparent physical attractiveness (based on a photograph or written description) is most influential in terms of the number of interested emails he or she receives. For example, men who report being six foot three or six foot four on their profiles receive more contact than average, while women seem to get the most attention when they are between five foot three and five foot eight. Meanwhile, red-haired men and gray- or short-haired women fare worse than average, and blondes or women with long, straight hair have an advantage.

  This creates the incentive to lie about appearances, and many users do so hoping to increase the number of potential matches interested in meeting them. Men will often add extra inches to their height, while women are likely to whittle off several pounds in their stated description. Thus not only are behavioral and other signals unavailable, but the information being used to judge a person’s potential suitability is often skewed.

  Still, do these observations constitute a significant hurdle to the future of relationships? Probably not. A positive interaction online will eventually lead to a real date offline where more reliable information can be conveyed, and daters quickly discover the truth. Additionally, the singles pool on the Web is larger than would occur in a physical setting, so even unintentionally weeding out some well-suited matches might not prove that much of a drawback. Finally, online dating has other benefits balancing out the eq
uation. For instance, if potential couples get to know each other adequately before going in for their first kiss, the chances of a positive connection may be improved since they are more comfortable together. Once partners have begun to develop a bond, the associated hormonal changes in their bodies boost the likelihood that a physical relationship will feel right.

  But it is still worth questioning how this relatively new trend may be affecting human courtship behavior, like kissing, that has evolved over millions of years to help identify a suitable mate. We may invest a significant amount of time learning about a person who’s not a good match. So in the end, the moment our lips touch probably reveals more about actual chemistry than weeks of accumulated emails. Still, at the very least, connecting online can increase our opportunities to get that close in the first place.

  And when it comes to new frontiers in romantic technology, dating websites are just the beginning. The gaming world is booming as platforms improve and virtual experiences become ever more interactive. For example, Second Life, the Internet’s largest user-created 3-D community, abounds with kisses between avatars in serious and casual relationships. Just as in the real world, kissing is a favorite activity in virtual life.

  In 2009, Nintendo DS debuted a Japanese computer game called Love Plus. It’s not the first dating video game, but its release raised eyebrows around the world as players were required to kiss their digital girlfriends. These kisses merely required tapping the screen with a stylus rather than a player’s actual lips, but the enormous popularity of Love Plus suggests that as engineering improves and computer graphics become ever more believable, there is an audience ready to embrace virtual relationships—quite literally—including the act of kissing an animated character.