Kissing Trumps Sex: Why How Often You Kiss Predicts Your Relationship Happiness Better Than How Often You Have Sex
- Terri DiMatteo, LPC
- 3 days ago
- 11 min read
Updated: 1 day ago
Educational content only. Not clinical advice. [Read full disclaimer→]
Do you remember a time when kissing was the most important thing? When you could lose yourself for an hour, and the entire world seemed to reduce itself to the space between your lips? When your knees turned weak, your heart gave a little jump, and you couldn't move away—and didn't want to?
Betty Everett sang it back in 1964, and Cher made it immortal in 1990: "Does he love me? I wanna know. How can I tell if he loves me so? Is it in his eyes? Oh, no! You'll be deceived. Is it in his sighs? Oh, no! He makes believe... It's in his kiss. That's where it is."
What turned out to be the case was that she was not only singing but also describing something that science would later prove, even though the research did not catch up for decades.
The data actually indicates that the frequency with which you kiss your partner is a better predictor of your level of happiness in the relationship than the frequency with which you have sex.
It's not just a little better or just a bit—kissing frequency predicts relationship quality at twice the strength of sexual satisfaction.
Between those initial days and the establishment of the habits associated with a long-term relationship, most couples stop kissing that way. Research indicates that one in five married couples gives up French kissing very early on and never takes it up again. About eight out of ten married couples no longer kiss each other regularly. One in five of them can go whole weeks without having a single kiss.
This is more than a minor loss; for the relationship bond, it represents a biological disaster.
The following explains what actually takes place in your body when you kiss deeply and passionately, as you did when everything was new—and what you lose when you stop.
The Microbiome Kiss: Your Bodies Are Literally Merging
A single ten-second kiss can transfer up to 80 million bacteria between you and your partner. That's not a problem—it's actually a benefit.
Research published in the journal Microbiome by Remco Kort and colleagues found that couples who kiss frequently share significantly more of their oral microbiota than strangers. Couples living together share about 38% of their tongue microbiome, compared to only about 3% in couples who don't cohabit. The more you kiss, the more your microbial ecosystems converge — becoming a shared biological environment.
If both partners are in good health, this transfer of bacteria serves as a mild immune challenge—akin to repeated, mild exposure to a wide variety of microbes, which helps train and enhance the immune system. This is analogous to the idea on which vaccination is based: controlled exposure leads to greater resilience. According to Kort's research, this subtle, continuous stimulation of the immune system may result in a stronger, more balanced immune response in the mouth and possibly elsewhere.
A healthy mouth microbiome helps prevent tooth decay and fights inflammation. Some researchers even think its benefits reach your gut and nervous system. The vagus nerve, which connects your gut and brain, can be stimulated by oral contact, helping your nervous system feel calmer and more regulated.
Your kisses are literally protecting you. They are protecting your health and your bond.
The Neurochemistry of a Deep Kiss: A Chemical Cocktail Designed to Strengthen Your Bond
A deep kiss isn't just about pleasure. It sets off a neurochemical chain reaction designed to bond you to your partner.
Dopamine floods your brain's reward system—the same one that lights up for food, gambling, even cocaine. It gives you a rush of euphoria, but more importantly, it makes you want to come back for more. That longing you feel after a deep kiss isn't just nostalgia; it's your brain's way of making sure you return to this person. The kiss feels good in the moment, but it also makes you want to seek out your partner again.
The neuropeptide oxytocin, which plays a key role in the formation of pair bonds in mammals, increases as a result of close physical contact. In the well-known experiments with prairie voles, females need to develop a partner preference following mating; oxytocin acts on receptors in the nucleus accumbens; if those receptors are blocked, then the bond does not form. In humans, the release of oxytocin when kissing leads to an increase in trust, closeness, and attachment — that is, the sense of belonging to someone.
Vasopressin, which is structurally similar to oxytocin, has a particularly important function in the formation of male pair bonds. In prairie voles — one of the very few mammalian species that mate for life — signaling of vasopressin in the ventral pallidum is essential for male individuals to develop the strong, exclusive partner preference which characterizes monogamy. The act of kissing reinforces that old instinct towards bonding and protection.
Serotonin has a mood-boosting effect while cortisol levels decrease; a study conducted at Lafayette College found that a 15-minute kiss was more effective than either talking or holding hands over the same period in reducing cortisol levels, leading to less stress, less conflict, and more connection.
Testosterone travels through saliva, especially increasing excitement — the longer and more passionately you kiss, the more is transferred.
This isn't just romance. It's your biology at work, building a bond that's older than language itself.
We're Not the Only Ones: Animals That Kiss to Bond
If you think deep kissing is just for humans, you haven't met bonobos. Bonobos — our nearest living relatives, along with chimpanzees — engage in full mouth-to-mouth kissing with the tongue, very similar to the human French kiss. This behavior is used in non-reproductive sexual situations, for settling disputes, for reinforcing social hierarchies, and for strengthening the bonds within their female-dominated groups. Bonnie de Waal and some other primatologists have recorded bonobos giving passionate kisses when making up after arguments — the kiss acting as a sort of reset for social tension, just as make-up kissing does in human couples.
Kissing frequency predicts relationship quality at twice the strength of sexual satisfaction.
Chimpanzees and gorillas are also seen engaging in affectionate mouth contact — including short lip touches, lip-smacking, and gentle nibbling — especially when grooming one another or after sharing food. A study conducted at Durham University in 2024 found that both chimpanzees and bonobos use hugs, kisses, and other forms of friendly physical contact to reassure one another before facing stressful situations, notably during disputes over food.
Smithsonian Magazine covered the same research and pointed out that great apes use kisses and cuddles to maintain peace—precisely what the study carried out at Arizona State University on human couples who increased the frequency of their kissing found: namely, less conflict, less arguing, and more connection.
In all primate species, mouth-to-mouth contact has two effects: it strengthens bonds, and it reduces tension. Does that sound familiar?
The message concerning evolution is clear: kissing is not merely a cultural addition, but an old form of bonding common to species that form pair bonds and social attachments. The deep kissing you do with your partner is therefore involving a mechanism which nature has been refining for millions of years—one that bonobos still use nowadays to keep their groups together.
What Evolutionary Psychology Says: The Kiss as Assessment and Bonding
Evolutionary psychologists have suggested three main functions of romantic kissing, and the research—most notably the 2013 study by Rafael Wlodarski and Robin Dunbar at the University of Oxford, which interviewed more than 900 participants—provided convincing evidence for two of these.
The assessment of suitability through kissing brings you close enough to pick up on olfactory and gustatory clues that might indicate genetic compatibility. In the well-known "sweaty T-shirt" experiments carried out by Claus Wedekind, women—especially during the time of ovulation—found the smell of men who had different MHC (Major Histocompatibility Complex) genes to be more pleasant. Since MHC genes are responsible for immune function, a preference for partners with different MHC alleles may have evolved to produce offspring with more robust immune systems.
Although more recent meta-analyses have cast doubt on the strength of this effect, the fundamental idea remains: kissing could serve as an unconscious biological method of screening and allow you to obtain information about a potential partner that your conscious mind cannot access.
The same Oxford study found that people with more sexual partners placed greater importance on 'kissing technique', specifically synchronization, indicating that the function of kissing varies with mating strategy.
The Oxford study's most striking finding was this: how often couples kiss is strongly linked to how happy they are together—more so than how often they have sex. In other words, the number of kisses is a better predictor of relationship happiness than the number of times you have sex.
Researchers call kissing an honest signal of commitment. It's risky: you share breath, saliva, and bacteria, and you get close. Only someone truly invested would do that. A kiss says what words can't: I trust you with my body.
Most telling of all, Wlodarski and Dunbar found very little evidence to show that the main purpose of kissing is to increase sexual arousal. Kissing isn't mainly intended as foreplay; its main purpose is to bond.
The Inverse Pattern: When Bonding Isn't the Goal
There's a telling pattern in how kissing behaves when the bonding incentive is removed.
In a casual hookup, where emotional attachment isn't the goal, deep kissing usually gets skipped or kept to a minimum. The same goes for transactional encounters—prostitution rarely involves full French kissing, across cultures and history. That's not a coincidence.
Think about it: if your body's goal is to avoid attachment—maybe to protect your heart, keep your distance, or separate intimacy from emotion—it knows what to do. You skip the kiss. Or you keep it light, just a quick peck.
This isn't about morality. It's about biology.
When scientists look at what sets hookups apart from long-term partnerships, one thing stands out: how often people kiss. Couples in committed relationships kiss more, kiss more deeply, and do it more often. In casual encounters, people kiss less, or not at all.
It's the flip side of the Arizona State University finding—the same mechanism, just working in reverse. When you want to bond, you kiss more. When you want to avoid bonding, you kiss less.
This pattern is powerful evidence: kissing isn't random. It doesn't just follow arousal (if it did, every hookup would include deep kissing). It lines up with whether you want to bond—or not.
So when you notice someone avoiding deep kissing, don't assume it's about technique or comfort. It's usually about something deeper: whether this person is meant to stay, pass through, or leave.
Kissing by the Numbers: Couples Who Kiss More Are Measurably Different
The most rigorous scientific evidence available on the effects of kissing comes from a study carried out by Boren and his colleagues. In the study, couples were told to raise their daily kissing frequency over a period of six weeks. The findings were:
Higher relationship satisfaction
Lower perceived stress
Decreased cholesterol levels
Less conflict and arguing
A study by Hanna-Walker and Busby, which involved 1,605 people in committed relationships, found that kissing frequency was a better predictor of relationship quality than sex frequency. In this study, having a partner who was regarded as a "good" kisser had twice the effect on relationship quality as sexual satisfaction.
Couples who kiss more frequently also report:
Higher sexual arousal
Greater likelihood of orgasm during sex
Lower anxious and avoidant attachment
Stronger feelings of secure attachment
The epidemiological finding reported by the ASU research was that husbands who kissed their wives before going to work lived, on average, up to five years longer than those who did not. Once again, this is a correlation, not causation — but the direction of the effect is in agreement with the points made above.
Here's one more statistic that should give every couple pause: one in five married couples gives up on French kissing from the start and never goes back. When you think about everything we've covered—the shared microbiome, the neurochemical bonding, the stress relief, the conflict reduction—giving up kissing is like taking out a load-bearing wall in your house and hoping it won't fall.
There's something darker in the data too — and you need to know it. When the Oxford team surveyed 900+ adults, they found that couples who kiss more cheat less. Not maybe, not possibly — inversely associated, they call it in research terms. In plain language: kissing is a safeguard for the bond. And here's what might sting for my betrayed partners reading this: 88% of women say kissing someone else is cheating. Not sex. Kissing. Only 73% of men agree. So if you're sitting there wondering whether that kiss mattered, here's the truth — for most women, it was the red line. The body knows when someone crossed the boundary of the bond, even if the mind tries to negotiate it away.
The Yearning: Why One Deep Kiss Always Leaves You Wanting More
Sixpence None the Richer expressed it exactly like that: "Kiss me beneath the milky twilight, lead me out onto the moonlit floor, hold your hand open, start the band and get the fireflies to dance, the sparkling silver moon — so kiss me."
You can see the longing expressed in that lyric: it doesn't say 'We kissed, and I was satisfied', but rather 'Kiss me' — an urgent and open-ended request which suggests that one kiss will never be enough. One kiss will never be enough.
It always comes back to the bond.
Dopamine doesn't merely produce a feeling of pleasure; it generates anticipation. The same neurochemical that makes a kiss seem transcendent also means that when it ends, you aren't satisfied but instead feel hungry and desire them again and again.
That's not a design flaw. That's the whole point.
Your craving for a deep kiss is your brain's way of making sure you come back to your partner. It's the same kind of reinforcement loop that bonds prairie voles for life. Every time they have intimate contact, reward chemicals fire, making them want to return to each other. The more contact, the stronger the bond. Each cycle makes the connection deeper.
Brian Hyland sang it in 1962: "I'll send you all my love, every day in a letter, sealed with a kiss." The kiss was the seal—the proof, the physical stamp which made the love real, not the words, but the kiss.
When couples stop deep kissing, they break the cycle. The dopamine-driven anticipation fades, oxytocin drops, and even the microbiome starts to drift apart. Your body forgets what your mouth once knew: this person is mine, and I am theirs. That longing isn't just teenage nostalgia—it's your biology keeping your bond alive.
What This Means for Your Relationship
Deep kissing isn't just for the start of a relationship. It's a living, ongoing way to keep your bond strong. It matters just as much for your relationship's health as emotional connection does.
In The Intimacy Bond framework, emotional and physical intimacy matter equally. Neither one has to come first, because both give you a sense of safety. A deep kiss brings both together at once: emotional closeness built on trust and vulnerability, and physical sensations—touch, taste, breath, and all the chemistry that comes with it.
Couples who keep kissing are the ones who keep bonding. Their bodies hold onto a connection that words alone can't keep alive.
So kiss like you mean it—because your body and relationship needs it. It truly does.
The Shoop Shoop Song had it right all along. It's in the kiss. That's where it is.
References and sources cited:
Kort, R., et al. (2014). "Shaping the oral microbiota through intimate kissing." Microbiome, 2:41.
Wlodarski, R. & Dunbar, R.I.M. (2013). "Examining the possible functions of kissing in romantic relationships." Archives of Sexual Behavior, 42(8), 1415-1423.
Boren, J.P., et al. (2009). "Kissing in marital and cohabiting relationships: Effects on blood lipids, stress, and relationship satisfaction." Santa Clara University Scholar Commons.
Hanna-Walker, V. & Busby, D.M. (2022). "A kiss is not just a kiss: kissing frequency, sexual quality, attachment, and sexual and relationship satisfaction." Sexual and Relationship Therapy.
Wedekind, C., et al. (1995). "MHC-dependent mate preferences in humans." Proceedings of the Royal Society B, 260, 245-249.
Hughes, S.M., Harrison, M.A., & Gallup, G.G. (2007). "Sex differences in romantic kissing among college students: An evolutionary perspective." Evolutionary Psychology, 5, 612-631.
de Boer, A., van Buel, E.M., & Ter Horst, G.J. (2012). "Love is more than just a kiss: A neurobiological perspective on love and affection." Neuroscience, 201.
Durham University (2024). Chimpanzee and bonobo physical contact studies. Reported via BBC and Smithsonian Magazine.
Terri DiMatteo, LPC
Founder Open Door Therapy l Creator of the Intimacy Bond Framework™
Specializing in couples counseling, affair recovery and healing from narcissistic abuse. Open Door Therapy offers individual and couples therapy, as well as personal consulting for those navigating a complex life dilemma.
