Kissing is an intimate experience that engages all of our senses and elicits powerful emotional and physical responses. When two people kiss, their brains release a cocktail of neurotransmitters and hormones that elevate mood, induce pleasure, and promote pair bonding. Let’s explore what’s really happening inside our brains when we kiss.
The Science of Kissing
Several studies have investigated the neurochemical factors involved in kissing. In a 2014 study published in the journal Brain and Cognition, researchers asked 51 couples to fill out questionnaires about their sex lives and provide saliva samples before and after kissing their partners. Analysis of the salivary bio-markers revealed that levels of cortisol (a stress hormone) decreased after kissing, while levels of oxytocin, serotonin, and dopamine increased.
Oxytocin, also known as the “love hormone,” is central to establishing social bonds and enhancing feelings of intimacy. An increase in oxytocin helps promote affection and attachment between partners.
Serotonin regulates mood, and higher levels induce euphoria and pleasure. Dopamine is another feel-good neurotransmitter associated with motivation, reward, and addiction. The release of dopamine during intimate acts reinforces behavior and helps couples form meaningful bonds.
Kissing Activates Reward Centers
Brain scanning studies also elucidate what goes on neurologically when couples kiss. In a 2005 study published in Archives of Sexual Behavior, researchers used positron emission tomography (PET) to scan the brains of 15 heterosexual couples while they kissed. Activation occurred in multiple cortical and subcortical brain systems, including:
- The reward system – areas like the ventral tegmental area (VTA) that regulate motivation and pleasure.
- The limbic system – areas like the amygdala and hippocampus that govern memory, emotion, and arousal.
- The frontal lobes – areas like the medial prefrontal cortex that mediate higher-order thinking.
The significant activation of dopaminergic reward centers suggests kissing is a pleasurable experience most people find rewarding. The engagement of limbic areas indicates it can also trigger emotional arousal and formation of memories associated with the kiss.
Kissing Lowers Cortisol and Blood Pressure
Kissing doesn’t just raise levels of feel-good hormones, it also lowers levels of the stress hormone cortisol. Cortisol is an important part of our biology – helping regulate metabolism, blood sugar, blood pressure, and inflammatory responses. But when chronically elevated, it can impair cognition, mood, and cardiovascular health.
Studies show kissing helps quell cortisol. In a 2009 study in Western Journal of Communication, researchers examined cortisol levels in heterosexual couples before and after saying goodbye by kissing or shaking hands. Cortisol levels decreased after kissing, but not after handshaking. The researchers concluded kisses function as important relationship maintenance behaviors.
Kissing also lowers blood pressure, which may partly explain why it reduces cortisol. In a 2014 study in the journal Nature, scientists monitored vital signs in 15 couples as they kissed and hugged for the first time after being reunited. Systolic blood pressure decreased during kissing but not hugging.
Different Kisses Activate Different Brain Regions
Not all kisses are equal – the way we kiss conveys distinct emotions and motivations. Passionate romantic kisses likely inspire much different brain activity compared to quick habitual kisses. Neuropsychologists at the University of Oxford sought to map these differences.
In a 2021 study in Personality Neuroscience, researchers asked 183 partners to fill out surveys about their kissing habits and the motivations behind them. They characterized kisses into three categories:
- Romantic/passionate kissing – long kisses associated with sexual desire and romantic love.
- Affectionate kissing – short comfortable kisses that communicate attachment.
- Habitual kissing – brief kisses with little thought or feeling.
Brain scans revealed each type of kiss triggered distinct patterns of activation:
| Kiss Type | Brain Regions Activated |
|---|---|
| Romantic/Passionate | Reward system, limbic system |
| Affectionate | Oxytocin and dopamine systems, medial prefrontal cortex |
| Habitual | Habit formation areas like caudate |
Romantic kisses closely paralleled the activation seen in earlier studies – triggering dopaminergic reward centers that regulate pleasure, focus, motivation. Affectionate kisses also activated oxytocin and dopamine systems associated with pair bonding.
Kissing Reduces Stress and Boosts Immunity
Given kissing lowers cortisol and blood pressure, it likely has direct stress-alleviating effects. Cortisol plays a key role in the hypothalamic-pituitary-adrenal axis – regulating stress responses, metabolism, and inflammation.
Chronically high cortisol can suppress immune function by lowering production of lymphocytes that combat pathogens. This is why stress is associated with increased susceptibility to the common cold and infections.
But the cortisol-lowering effects of kissing may help boost immunity. In a 2020 study in Life Sciences, researchers examined changes in salivary cortisol, IgA antibody levels, and self-reported stress in 52 couples after kissing. Kissing increased IgA levels while lowering cortisol, suggesting it enhances mucosal immunity while curbing stress.
Kissing May Boost Self-Esteem and Reduce Depression
The flood of dopamine and oxytocin released while kissing doesn’t just increase pleasure – it also enhances mood and self-esteem. Studies show positive social interactions are pivotal for emotional health and can help alleviate depression.
In a 2017 study in Emotion, researchers randomly assigned 96 heterosexual undergrads to kiss their romantic partners for 15 minutes or engage in small talk. Afterwards, those who kissed had lower levels of the stress hormone cortisol and reported less depressive feelings.
The authors concluded kissing may be an effective way to boost mood and mental health. The sensory stimulation combined with release of feel-good chemicals during kissing likely counteracts negative emotional states.
Kissing Facilitates Pair Bonding
While kissing offers health perks for individuals, it also promotes relationship quality and pair bonding between partners. The oxytocin and dopamine released while kissing enhances feelings of intimacy and affection for a partner.
In a 2009 study in Psychiatry Research, researchers examined fMRI brain scans of young couples kissing and found activation of areas linked to pair bonding and social cognition. This suggests passionate kissing facilitates attachment within relationships.
Studies also show couples who kiss frequently are more satisfied with their relationships. In a 2013 study published in Archives of Sexual Behavior, over 1000 couples completed surveys about their sex lives, kissing habits, and relationship satisfaction. More frequent kissing was associated with higher relationship satisfaction among couples.
Kissing May Boost Self-Esteem and Reduce Depression
The flood of dopamine and oxytocin released while kissing doesn’t just increase pleasure – it also enhances mood and self-esteem. Studies show positive social interactions are pivotal for emotional health and can help alleviate depression.
In a 2017 study in Emotion, researchers randomly assigned 96 heterosexual undergrads to kiss their romantic partners for 15 minutes or engage in small talk. Afterwards, those who kissed had lower levels of the stress hormone cortisol and reported less depressive feelings.
The authors concluded kissing may be an effective way to boost mood and mental health. The sensory stimulation combined with release of feel-good chemicals during kissing likely counteracts negative emotional states.
Kissing Facilitates Pair Bonding
While kissing offers health perks for individuals, it also promotes relationship quality and pair bonding between partners. The oxytocin and dopamine released while kissing enhances feelings of intimacy and affection for a partner.
In a 2009 study in Psychiatry Research, researchers examined fMRI brain scans of young couples kissing and found activation of areas linked to pair bonding and social cognition. This suggests passionate kissing facilitates attachment within relationships.
Studies also show couples who kiss frequently are more satisfied with their relationships. In a 2013 study published in Archives of Sexual Behavior, over 1000 couples completed surveys about their sex lives, kissing habits, and relationship satisfaction. More frequent kissing was associated with higher relationship satisfaction among couples.
Kissing Can Be Addictive
Given kissing activates the brain’s reward system, it has an addictive quality. In a 2014 study published in Psychiatry Research, researchers scanned the brains of 153 young adults while they looked at photos of their romantic partners. Brain activation patterns reflected those seen in other addictive behaviors.
The caudate nucleus, a region involved in reward and motivation, showed increased activation when participants viewed photos of their loved ones. But there was less activation in areas like the amygdala linked to unpleasant stimuli.
According to the researchers, falling in love elicits addiction-like brain patterns similar to when substance abusers view drug paraphernalia. The craving for emotional union with the beloved activates the same dopamine-rich neural pathways that promote drug seeking.
Kissing May Reduce Allergic Responses
Allergic reactions occur when the immune system identifies harmless particles as threats. But studies show kissing may help reduce sensitivity to potential allergens. Saliva contains proteins that help mitigate allergenic reactions.
In a 2014 study in Journal of Sexual Medicine, researchers asked 24 women and their partners to collect saliva samples before and after periods of kissing and no kissing. Compared to the no-kissing state, salivary proteins were significantly higher after kissing, indicating swapping spit during kissing exposes people to allergens that help build tolerance.
In a way, frequent kissing may act like a natural allergy shot that decreases hypersensitivity. The immunoglobulin antibodies found in saliva help counteract pollen, animal dander, dust mites and other allergens.
Kissing Can Spread Infections
While kissing can boost immunity, intimate physical contact also facilitates transmission of bacteria, viruses, and other pathogens between partners. Saliva contains over 700 species of microbes that can lead to oral disease or respiratory infections when swapped.
Among couples, kissing often spreads viruses that cause:
- Common cold
- Flu
- Mononucleosis (Mono)
- Herpes simplex virus 1 (HSV-1)
- Strep throat
- Meningitis
A 10-second intimate kiss can transfer as many as 80 million bacteria between mouths. Viruses may enter the body through tiny cuts or sores in the mouth and throat. Herpes and other pathogens can also be transferred through infected saliva.
How Kissing Changes Through Relationships
Kissing fulfills different needs at different relationship stages. In new relationships, it helps assess mate suitability and promotes bonding.
In a 2007 study in Archives of Sexual Behavior, nearly 900 undergrads detailed their recent kissing experiences. Frequent kissing was more common in new relationships compared to long-term relationships. It suggests kissing plays a greater evaluative role in initial courtship.
But kissing remains important for established couples – helping maintain intimacy and satisfaction. Over 90% of couples continue to kiss even after being together for many years. Overall, egalitarian couples who view kissing as mutually gratifying tend kiss more often and report greater relationship quality.
While kissing less may not doom relationships, couples who stop entirely risk losing an important source of pleasure and bonding.
Cultural Differences in Kissing
While kissing seems intuitive, cultural norms shape when, where, and how it occurs. Europeans and North Americans frequently kiss as a greeting or display of affection. But in parts of Asia, Africa, and the Middle East, it remains taboo.
Some key cultural differences:
- American and European couples often kiss publicly and privately.
- In China and Japan, public kissing is widely unacceptable.
- Some Islamic cultures prohibit kissing between unmarried couples.
- In India, kissing is generally reserved for married couples and done only privately.
Anthropologists believe the kiss-taboo in some regions may stem from past associations with promiscuity. But cultures have evolved, and kissing is becoming more normalized worldwide.
Conclusion
Kissing is a uniquely human behavior that evolved as a courtship and pair bonding mechanism. When we kiss, we engage in an intimate neurochemical exchange that boosts mood, reduces stress, and promotes social attachment.
While kissing offers health and relationship benefits, overuse within new relationships may indicate unhealthy attachment patterns. But between established partners, it remains a simple way to express love and affection.
Overall, moderate romantic kissing strengthens emotional bonds between partners and offers a range of psychological and physiological advantages. Our brains seem hardwired to enjoy this intimate ritual.