The Science of Kissing Summary

Why do we kiss? It’s not just about romance—it’s biology, evolution, and even a little bit of chemistry.

1. Kissing Starts with Our Earliest Experiences

From the moment we’re born, our lips play a key role in how we experience the world. Nursing is one of the first comforting sensations a baby feels, creating a connection between lip contact and feelings of love and security. This association is deeply ingrained in our biology.

The act of nursing involves the same lip movements as kissing, and it happens in a safe, nurturing environment. Over time, this connection between lip contact and comfort becomes a foundation for how we express affection later in life. Even premastication, the ancient practice of feeding babies mouth-to-mouth, reinforces this bond. Though it may seem strange today, it was once a practical way to transition babies from breastfeeding to solid food.

This early connection isn’t unique to humans. Many animals, like apes and birds, also use mouth-to-mouth feeding to nurture their young. These behaviors create a biological link between lip contact and positive emotions, laying the groundwork for kissing as a universal expression of love and trust.

Examples

• Babies instinctively purse their lips for nursing, mimicking the motion of kissing.
• Premastication was practiced in ancient Egypt and is still used in some modern communities.
• Apes and birds also engage in mouth-to-mouth feeding to bond with their offspring.

2. Kissing Is a Universal Social Tool

Kissing isn’t just about romance—it’s a way to communicate and build relationships. Throughout history, humans have used kissing for various purposes, from sealing contracts to showing respect. In the Middle Ages, people kissed documents marked with an “X” to signify agreement, a tradition that lives on in how we use “X” to represent kisses today.

Social kissing also reflects hierarchy and status. For example, people in medieval Europe would kiss a priest’s robe or the Pope’s ring as a sign of reverence. This practice isn’t limited to humans; animals also engage in kiss-like behaviors to strengthen bonds and exchange information. Bonobos, for instance, kiss with their lips and tongues, while cats lick each other and porcupines nuzzle.

These behaviors, whether in humans or animals, serve to build trust and foster connection. By entering each other’s personal space, individuals signal acceptance and strengthen their social ties.

Examples

• In medieval Europe, kissing was used to greet people of higher status, like priests or kings.
• Bonobos kiss with their lips and tongues, much like humans.
• Ground squirrels brush noses, and turtles tap each other’s shells as forms of bonding.

3. Kissing Helps Us Choose the Right Partner

Kissing isn’t just romantic—it’s a biological test. When we kiss, we subconsciously assess a potential partner’s genetic compatibility. This is largely influenced by scent, which carries information about a person’s immune system.

Our immune system is shaped by MHC (major histocompatibility complex) genes, and we’re naturally drawn to partners with different MHC genes. This diversity strengthens the immune system of potential offspring. A famous study by Claus Wedekind demonstrated this: women preferred the scent of men whose MHC genes were most different from their own.

This biological mechanism explains why some kisses feel “off.” If a partner’s scent signals genetic similarity, like a family member’s, the kiss may feel wrong. This subconscious process helps us make better choices for reproduction and the health of future generations.

Examples

• MHC gene diversity leads to stronger immune systems in offspring.
• Claus Wedekind’s study showed women preferred the scent of genetically different men.
• In Back to the Future, Lorraine’s kiss with Marty felt wrong because of their genetic similarity.

4. Kissing Triggers a Natural High

Kissing doesn’t just feel good—it activates the brain’s reward system. When you kiss, your body releases a cocktail of chemicals, including adrenaline, serotonin, and dopamine. These chemicals create feelings of euphoria, relaxation, and excitement.

This chemical rush is similar to the effects of drugs like cocaine, which also stimulate the brain’s reward centers. The dopamine released during a kiss can even make you crave more, creating a sense of addiction to your partner. Over time, this initial high fades, but other chemicals, like oxytocin, take over to build long-term bonds.

Kissing also has physical benefits. It deepens your breath, dilates blood vessels, and lowers cortisol levels, reducing stress and improving overall health. In this way, kissing is both a short-term thrill and a long-term health booster.

Examples

• Dopamine creates feelings of euphoria and craving, similar to cocaine.
• Oxytocin strengthens emotional bonds and is released during kissing and orgasms.
• Kissing lowers cortisol, reducing stress and improving heart health.

5. Kissing Strengthens Emotional Bonds

Kissing isn’t just about passion—it’s a way to build lasting connections. Oxytocin, often called the “love hormone,” is released during kissing, deepening emotional bonds between partners. This hormone plays a key role in long-term relationships, helping couples stay connected even as the initial spark fades.

Oxytocin also strengthens bonds between family members. For example, parents and children release oxytocin when they kiss or hug, reinforcing their emotional connection. This hormone is a biological tool for maintaining close relationships over time.

While dopamine fuels the excitement of new love, oxytocin ensures that relationships endure. This balance between short-term passion and long-term attachment is what makes kissing such a powerful tool for connection.

Examples

• Oxytocin is released during kissing, hugging, and orgasms.
• Parents and children bond through physical affection, which releases oxytocin.
• Long-term couples rely on oxytocin to maintain their emotional connection.

6. Kissing Is a Gateway to Reproduction

Kissing plays a key role in human reproduction by fostering lust, attraction, and attachment. Lips are packed with nerve endings that stimulate the brain’s limbic system, which governs emotions like love and desire. This makes kissing a natural precursor to sex.

Interestingly, men and women may use kissing differently. Women often use it as a way to assess a partner’s suitability, while men may use it to increase the likelihood of sex. For example, men prefer open-mouth kisses, which transfer testosterone and may boost a woman’s libido.

Despite cultural attempts to ban kissing, it remains a fundamental part of human behavior. From the Kama Sutra to modern science, kissing is recognized as a key step in the process of reproduction.

Examples

• Lips stimulate the limbic system, triggering feelings of love and lust.
• Men transfer testosterone through open-mouth kisses to increase arousal.
• The Kama Sutra dedicates an entire chapter to the art of kissing.

7. Kissing Is a Cross-Cultural Phenomenon

While kissing is common, it’s not universal. Some cultures don’t practice romantic kissing at all, while others place great importance on it. This variation shows that kissing is both a biological instinct and a cultural expression.

In societies where kissing is common, it often carries deep emotional and social significance. In others, affection may be expressed through different behaviors, like nuzzling or sniffing. These differences highlight the adaptability of human connection.

Despite these variations, the underlying purpose of kissing—building bonds and assessing compatibility—remains the same. Whether through a kiss or another gesture, humans find ways to connect and communicate.

Examples

• Some cultures, like the Mehinaku in Brazil, don’t practice romantic kissing.
• In many Asian cultures, public displays of affection, including kissing, are discouraged.
• Bonobos use kissing as a way to resolve conflicts and strengthen social bonds.

8. Kissing Has Health Benefits

Kissing isn’t just good for your relationships—it’s good for your health. It lowers cortisol levels, reducing stress and improving heart health. It also boosts your immune system by exposing you to your partner’s bacteria, which can help you build resistance to illnesses.

Kissing can even burn calories, though not as many as more vigorous activities. A passionate kiss can burn up to 6 calories per minute, making it a fun way to stay active. These health benefits make kissing a simple yet effective way to improve your well-being.

Examples

• Kissing lowers cortisol, reducing the risk of heart disease.
• Exchanging bacteria during kissing boosts your immune system.
• A passionate kiss burns up to 6 calories per minute.

9. Kissing Is Resilient to Change

Despite attempts to ban or discourage kissing, it has persisted throughout history. From the Great Plague to modern health scares, societies have tried to limit kissing for fear of spreading disease. Yet, it remains a natural and enduring part of human behavior.

This resilience shows that kissing is more than just a habit—it’s a fundamental part of who we are. It fulfills biological, emotional, and social needs, making it an irreplaceable aspect of human connection.

Examples

• Kissing was banned during the Great Plague in London to prevent disease spread.
• South Africa attempted to ban kissing among minors in 2008 to curb HIV.
• The Catholic Church tried to outlaw kissing for moral reasons but failed.

Takeaways

1. Build anticipation before a kiss to heighten the experience and deepen your connection.
2. Use kissing as a way to reduce stress and strengthen your emotional bonds with loved ones.
3. Pay attention to how a kiss feels—it might reveal more about your compatibility than you realize.