The Science of Kissing Summary and Review

by Sheril Kirshenbaum

Has The Science of Kissing by Sheril Kirshenbaum been sitting on your reading list? Pick up the key ideas in the book with this quick summary.

Kissing is important in our romantic relationships. Could you imagine a Hollywood movie depicting a passionate love story without at least a couple of intimate kissing scenes? However, as you’ll learn from this book summary, there’s more to the art of kissing. Not only does it fulfill several different functions for humans and our communities, most animals – even porcupines – like to kiss too, and for a good reason. This book summary will update you on the science of kissing, including what we now understand about kissing’s interesting effects on our brain and health.

In this summary of The Science of Kissing by Sheril Kirshenbaum, you’ll also discover:

  • why we use an “X “to signify a kiss in texts and online chat, and how it correlates to the Middle Ages;
  • how kissing can operate in a similar way to a genetic test; and
  • What the connection is between kissing and cocaine.

The Science of Kissing Key Idea #1: Associations of Lip Contact 

Almost everyone enjoys kissing, but we rarely stop to wonder why that is. The answer is deeply rooted in our biological makeup One of the first physically enjoyable sensations that we experience as humans is nursing; using our lips comes naturally. Babies suck their thumbs even in the womb and purse their lips for nursing as soon as they’re born – which is the same lip movement as kissing. Nursing is quite soothing for infants. It usually occurs in a safe and calm environment, and consequently, the baby grows to associate soft pressure on the lips with feelings of security and love. Premastication, the method of feeding mouth-to-mouth, was considered the most practical way to feed babies and toddlers for thousands of years, and also biologically linked positive feelings to lip contact. Premastication might sound a bit gross to us now. However, mechanically mashed baby food is a rather recent invention, and pre-chewed food used to be the best way to transition infants out of breastfeeding. Other animals, such as apes and birds use premastication too, and humans still use it in a few regions. The first known written records of this method date back to ancient Egypt. One study found that 39 out of the 119 investigated modern communities continue to practice premastication for multiple purposes including feeding, ritual, and circumstances such as disease prevention. Premastication doesn’t just increase a baby’s feelings of security, attachment, and love. It also helps to shift the positive association of mouth-to-breast contact to mouth-to-mouth contact. This process further strengthens the emotional and behavioral foundation for kissing that we develop later in life. Our penchant for kissing isn’t only about feeling love; find out more in the next book summaries!

The Science of Kissing Key Idea #2: What Kiss-Like Behaviors Mean For Humans and Animals

Are you aware of why we use the letter “x” to denote kissing? There’s a historical reason behind the choice. Throughout history, humans have employed kissing for numerous reasons. In the Middle Ages, it was regularly used to seal contracts. The place on the contract that was kissed by the involved parties was marked by an “x,” similarly to how we use “x’s” for kisses in online chats today. So we’ve represented kissing like this for hundreds of years. People in the Middle Ages also used kissing as a mark of social status which was determined by where you would kiss someone upon greeted them. When a person greeted a priest, they kissed the cloth of his robe, or with the Pope, they kissed his slippers or ring. People would even kiss the ground when greeting a king. This variety of social kissing is common in the animal kingdom as well. Nearly every animal species has a behavior similar to kissing, whether it’s caressing, sniffing or nibbling. Ground squirrels brush noses, moles rub snouts, turtles tap each other’s hearts, cats lick each other and porcupines nuzzle. Bonobos, humans’ closest relative in the animal world, kiss using lips and tongues, just like we do. Whatever “kissing” method an animal utilizes allows them to exchange information and strengthen relationships. Researchers will never know the animals’ exact thoughts, but it’s clear that kiss-like behaviors signal trust and acceptance between those that use them. “Kissing” requires entering into personal space and exchanging sensations of taste, touch, and smell. Kissing also serves various other purposes for animals, just as it does for us. A “kiss” between potential mates might signify a willingness to mate, where a “kiss” between family members or members of the same social group means something completely different.

The Science of Kissing Key Idea #3: Kissing and Compatibility

In the film Back to the Future, the main character travels back in time and accidentally prevents his parents from meeting by making his mother fall in love with him. However, when she kisses him, it doesn’t feel right to her. She says, “It’s like I’m kissing my brother! That particular scenario is fictional, but the biology behind it is quite real. Each human and ape has a unique scent because of the unique glands in our neck, face, armpits and genital area. When we’re looking for a mate, we seek out one with a smell that differs from ours. We’re more likely to produce healthy offspring with someone who’s biologically and immunologically dissimilar to us. One group of genes that plays a pivotal role in our immune system is MHC genes, which help us to distinguish our cells from foreign attackers. The more diverse our MHC genes are, the more robust our immune system is. MHC genes are a combination of your parents’ MHC genes. So, parents with very different MHC genes tend to produce offspring with a robust immune system. All of this indicates we naturally prefer mates who have a smell suggesting their MHC genes are different than ours. Claus Wedekind conducted an important study on this phenomenon in 1995. He had female participants smell t-shirts worn by several men and asked them each to select the shirt with the scent they found most attractive. The women subconsciously chose shirts from the men with MHC gene sets that were the most distinct from their own. That’s why it felt wrong for the mother in Back to the Future to kiss her son romantically. Even though she wasn’t aware of what was happening, her body could sense that he was too biologically similar to her; he didn’t smell like a prospective mate.

The Science of Kissing Key Idea #4: Why Kissing is Healthy

If you’ve ever kissed someone, you’ve encountered a similar type of high that people get when taking drugs like cocaine. Your brain receives a rush of energy and a natural high when you’re kissing someone. As you kiss, your breathing gets deeper, and your blood vessels dilate, making you flush and sending more oxygen to your brain. Next, the brain releases chemical messengers that make you feel “high.” Those include adrenaline, which increases energy and heart rate; serotonin, which causes you to feel relaxed; and dopamine, which makes you euphoric and leaves you craving more. That’s why you can grow to feel addicted to kissing your partner; it stimulates the same brain regions as cocaine! Researchers have also discovered that serotonin levels of people who’ve recently fallen in love are similar to serotonin levels of people with obsessive-compulsive disorders. That is likely why we often feel like we “obsess” so much when we have a new lover. Your body also releases bonding hormones and reduces your stress when you kiss, which makes kissing a positive deed healthwise too. Kissing releases oxytocin, the “love hormone” or “bonding hormone” that strengthens emotional attachments, particularly with lovers and relatives. The effect of dopamine doesn’t last that long, which is why your sexual desire for a partner can diminish over time. Although, oxytocin does enable us to build relationships that last for decades. Oxytocin is also responsible for the feelings of pleasure that women experience during orgasm. Men and women can reach up to five times the normal levels of oxytocin while climaxing. Kissing also lowers cortisol levels, the “stress hormone” that increases blood pressure and weakens immune systems. Chronically high levels of cortisol are dangerous and contribute to health issues such as heart disease, so anything that reduces cortisol is good. Overall, kissing can function as a drug for the short term, but it additionally strengthens bonds in the long run.

The Science of Kissing Key Idea #5: How Kissing Facilitates Reproduction

You’ve probably heard of the Kama Sutra, the famous guide to sex, love, and marriage, originating from the Hindu tradition. There is an entire chapter devoted to the topic of kissing in it. Contemporary science also recognizes the importance of kissing, just like the Kama Sutra does. It’s a component of our evolution: kissing fuels the sex drive thus making someone more likely to reproduce. Lips have many sensitive nerve endings that stimulate our limbic system, the portion of the brain associated with love, lust, and passion. Interestingly, men and women may kiss for varying purposes. Women often to use kissing as a test of sorts, to determine if sex is even an option with a potential lover. One survey found that seven out of eight women wouldn’t even consider sex unless they had kissed that person first. Men tend to approach things differently. Studies have shown that men prefer kissing that involves more tongue. Some scientists theorize that it’s because it increases the chances of a woman having sex with them, being that tongue kisses transfer more testosterone to a woman. Kissing is a piece of our biological legacy. Though various societies have attempted to ban it, kissing has always been around. Various rulers and governments sought to outlaw kissing for health reasons, like during the Great Plague of London in 1665. A law in South Africa tried to restrict children who were under the age of 16 from kissing as recently as 2008, in a misguided effort to control the spread of HIV. The Catholic Church tried to forbid kissing numerous times for moral reasons and also because it can lead to people having sex. Regardless, none of their attempts were successful; kissing is a natural part of who we are.

The Science of Kissing Key Idea #6: In Review

The key message in this book: Kissing is an element of our biology and evolution, which is why it’s so fundamental for humans and animals. It strengthens our social bonds, makes us healthier and happier, assists us in finding a suitable mate and encourages us to reproduce. Kissing is far more than merely a nice feeling! Actionable advice: Create anticipation. It may sound like an idea from a cheesy romance novel, but science backs this concept up. If, when getting to know someone, you cultivate anticipation before kissing, you build your dopamine levels, which creates a more rewarding experience when the kiss finally happens. Suggested further reading: Come as You Are by Emily Nagoski Come as You Are (2015) is a scientific guide about the art and beauty of sex. This book summary explains how loving your body and exploring pleasure beyond social norms can open new doors to euphoric satisfaction.