Cheating almost never comes down to a single cause. Research on infidelity points to a mix of factors: personality traits, attachment style, relationship dissatisfaction, opportunity, and evolved psychological pressures most people aren’t consciously aware of.
Depending on the survey, somewhere between 1 in 10 and 1 in 5 people in a monogamous relationship report having been unfaithful at least once. Understanding why it happens doesn’t excuse it. It explains it, which is usually the first thing couples and individuals need before deciding what comes next.
What Counts as Cheating?
There’s no single legal or clinical definition. Researchers generally use the term extradyadic involvement to cover any romantic or sexual activity outside an agreed-upon exclusive relationship, and that umbrella covers more than physical sex.
Emotional affairs (deep intimacy and secrecy with someone outside the relationship, without physical contact) are a well-documented category in their own right, and many people rate them as just as painful to discover as a physical affair.
A newer category is getting attention too. A January 2026 Bankrate survey found that 43 percent of U.S. adults consider hiding financial secrets from a partner (a second credit card, a hidden loan, an undisclosed account) to be at least as bad as physical infidelity, and close to half of couples said they don’t know all of their partner’s financial details. Cheating, in other words, comes down to which agreements a couple has actually made and which ones got broken, not one fixed behavior.
How Common Is Infidelity, Really?
More common than most people expect, though the exact number moves depending on how you ask and when the survey was taken. The most consistent long-term data comes from the University of Chicago’s General Social Survey, which has tracked infidelity since 1972.
Across recent decades, it has found that roughly 20 percent of married men and 10 to 15 percent of married women report having had sex outside their marriage at least once, though more recent research suggests that gap between men and women has been closing.
Other surveys land in a similar range: one frequently cited estimate puts lifetime infidelity at 10 to 13 percent of adults, with a peak of around 20 percent among couples in their 40s.
Nearly every researcher in this space adds the same caveat: these are self-reported numbers about a behavior most people have a strong incentive to hide, even in an anonymous survey, so most treat the real rate as a floor rather than an accurate ceiling.
What Causes Infidelity? The Leading Theories
No single trait or circumstance reliably predicts who will cheat. Researchers who study infidelity generally sort the contributing factors into a few overlapping categories.
Individual Traits and Relationship Factors
A widely cited review by researchers Charlene Belu and Lucia O’Sullivan sorted decades of infidelity studies into three buckets: individual traits, relationship dynamics, and situational opportunity.
On the individual side, personality research consistently links a lower score on conscientiousness (the trait tied to self-discipline and impulse control) with a higher risk of infidelity, along with higher extraversion and higher neuroticism. People who score high on the so-called Dark Triad traits (narcissism, manipulativeness, and a callous disregard for others) also turn up more often in infidelity research.
Relationship factors mattered more than personality in Belu and O’Sullivan’s review. Dissatisfaction within the relationship, more than any single personality trait, was the strongest predictor they found.
Opportunity matters too: simply having regular access to an attractive alternative, through work, a shared social circle, or a hobby, raises the odds independent of how happy someone is at home.
The Reasons People Give, in Their Own Words
A University of Maryland study published in the Journal of Sex Research took a more direct approach: researchers asked 562 adults who admitted to cheating why they did it.
Their answers clustered into eight recurring motivations: anger or a wish for revenge, low self-esteem, a search for variety, falling out of love, feeling neglected, low commitment to the relationship, unplanned situational circumstances, and sexual desire.
The same study found a gender split in emphasis. Men were more likely to point to sexual desire, variety, and situational opportunity. Women were more likely to point to feeling neglected. That doesn’t mean the reasons are exclusive to one gender; it means the average emphasis differed across the sample.
Attachment Style: The Anxious and Avoidant Connection
Attachment theory, originally developed to describe the bond between infants and caregivers, turns out to predict a fair amount about adult infidelity too.
A 2023 meta-analysis pooling 17 studies and more than 13,600 participants found a small but statistically reliable link between insecure attachment and marital infidelity, strongest among people with fearful or dismissive attachment patterns.
A separate line of research gets more specific about the mechanism. Across eight linked studies, researchers led by C. Nathan DeWall found that people high in avoidant attachment (people who keep emotional distance and resist depending on a partner) paid more attention to attractive alternatives, rated those alternatives more positively, and felt less committed to their current relationship, a chain that predicted more infidelity over time. The effect wasn’t so much about a lack of love as a lower baseline investment in the relationship’s exclusivity.
The Evolutionary Psychology Angle
Evolutionary psychologists, most prominently David Buss, argue that both long-term pair-bonding and occasional infidelity may have offered reproductive advantages under different ancestral conditions, which is one reason the behavior persists across nearly every human culture despite near-universal social rules against it.
The same research tradition uncovered a heavily replicated asymmetry. In studies going back to 1992, men consistently report more distress imagining a partner’s sexual infidelity, while women consistently report more distress imagining a partner’s emotional infidelity.
Buss and colleagues explained this through differing evolutionary stakes: sexual infidelity historically threatened a man’s certainty about his own paternity, while emotional infidelity threatened a woman’s access to a partner’s long-term commitment and resources.
The theory remains genuinely contested. Critics argue that modern social and economic conditions can explain the same jealousy pattern without invoking deep evolutionary history, and some more recent replications find the sex difference smaller than the original studies suggested.
Esther Perel’s Reframing: Affairs and the Self
Not every explanation fits neatly into a personality trait or an evolutionary pressure. Psychotherapist Esther Perel, author of The State of Affairs and Mating in Captivity, has spent decades treating couples after infidelity, and her clinical experience adds a different layer. In her telling, most of the people she sees are not serial cheaters. Something more specific set them off, often unrelated to how happy the relationship actually was.
Perel argues that many affairs are less about wanting to leave a partner and more about wanting to reconnect with a version of oneself that feels lost, often around milestones that raise questions of mortality or stagnation: a new decade of age, a parent’s death, a plateau at work.
The pull, in her framing, often has less to do with the other person and more to do with how alive the affair makes the unfaithful partner feel. Her 2015 TED talk on the subject has been viewed more than eight million times, making her one of the most publicly influential voices on this question.
Hard data backs up part of her milestone-age observation from a different angle. A 2014 study published in the Proceedings of the National Academy of Sciences, using data from more than 8 million users of an infidelity-focused dating site, found that men turning 29, 39, 49, or 59 (ages right before a new decade) were 18 percent more likely to be registered on the site than chance would predict.
The researchers linked the pattern to the same kind of milestone-driven searching for meaning that Perel describes in her clinical work, even though neither line of research set out to test the other.
Is Cheating a Sign Something Is Wrong With a Person?
Not necessarily, and not in a clinical sense. Unlike some topics this kind of research touches, infidelity itself has no entry in the DSM-5. It’s a behavior, not a diagnosis, and plenty of people with no diagnosable condition at all have cheated at least once.
That said, two things are worth separating. First, understanding the psychology behind infidelity is not the same as excusing it. A cause is not a justification, and none of the research above changes the fact that breaking an agreed-upon exclusivity is a real breach of trust with real consequences for the betrayed partner.
Second, repeated or compulsive infidelity, especially when someone feels unable to stop despite real consequences, is something some therapists treat as closer to a compulsive pattern than a series of unrelated choices. That framing is debated within the field and isn’t an official diagnosis, but it’s common enough that couples’ and individual therapists are trained to recognize it.
One data point worth knowing either way: people who have cheated in a past relationship are reportedly about three times more likely to do so again in a future one, compared with people who haven’t. Past behavior isn’t destiny, but it is information.
Read Also: What is the Psychology Behind Self-Harm: What Research Actually Shows | What is the Psychology Behind Foot Fetishes: What Research Actually Shows
Frequently Asked Questions
No. Relationship dissatisfaction is one of the strongest predictors researchers have found, but individual personality traits, attachment style, opportunity, and even a personal identity crisis unrelated to the relationship (as therapist Esther Perel has documented) can all lead to infidelity on their own.
Research most consistently links lower conscientiousness (less self-discipline and impulse control), higher extraversion, higher neuroticism, and Dark Triad traits like narcissism to a greater risk of infidelity. These are statistical patterns across large groups, not a diagnosis or a guarantee about any one individual.
Most large surveys, including the long-running General Social Survey, have found men reporting infidelity somewhat more often than women, though the gap has narrowed in more recent research. Reported motivations also differ by gender on average: men cite sexual desire and variety more; women cite neglect more.
Often, yes. Couples therapists who specialize in infidelity, including Esther Perel, report that many relationships not only survive an affair but go on to become more honest and satisfying than before, provided both partners are willing to do the difficult work of rebuilding trust.
Not in a simple, deterministic sense. Attachment style and personality traits shift the odds, and evolutionary psychologists argue humans evolved dispositions toward both monogamy and occasional infidelity. None of that removes a person’s choice in any specific instance.
The Bottom Line
Cheating isn’t one behavior with one cause. It’s a label applied to a wide range of situations, from a single situational lapse to a longer pattern rooted in attachment wounds or an unhappy relationship, and the research reflects that range rather than resolving it into a tidy answer.
What’s consistent across the theories is this: infidelity is rarely only about sex, it’s frequently more about the relationship (or the self) than about any particular partner, and understanding the psychology behind it is a tool for repair and honest decision-making, not a verdict on anyone’s character. If it’s affecting your own relationship, a therapist who specializes in infidelity, rather than general couples counseling, tends to get better outcomes.
Sources
- Why Do People Cheat? UMD Research Identifies 8 Motivating Factors. University of Maryland.
- Belu, C. F., & O’Sullivan, L. F. The science of infidelity: key psychological and contextual factors that predict cheating, as summarized by PsyPost.
- Infidelity. Psychology Today.
- 8 Reasons Why Partners Cheat. Psychology Today.
- Buss, D. M., Larsen, R. J., Westen, D., & Semmelroth, J. (1992). Sex differences in jealousy: Evolution, physiology, and psychology. Psychological Science, 3, 251-255.
- Buss, D. M. (2018). Sexual and emotional infidelity: Evolved gender differences in jealousy prove robust and replicable. Perspectives on Psychological Science.
- The interplay of attachment styles and marital infidelity: A systematic review and meta-analysis. PMC.
- DeWall, C. N., et al. (2011). So far away from one’s partner, yet so close to romantic alternatives: Avoidant attachment, interest in alternatives, and infidelity. Journal of Personality and Social Psychology, 101(6), 1302-1316.
- As Marriage Standards Change, A Therapist Recommends ‘Rethinking Infidelity.’ NPR.
- Infidelity Lurks in Your Genes. Richard A. Friedman, New York Times, republished via Columbia University.
- Financial Infidelity Survey 2026. Bankrate.
- Study highlights people most likely to cheat (reporting on a 2014 Proceedings of the National Academy of Sciences study). Fox News.
Hijab Zehra is an MPhil-qualified clinical psychology professional with an academic background in mental health, emotional wellbeing, behavioural patterns and psychological assessment. Her work focuses on helping individuals understand anxiety, mood changes, stress responses, emotional regulation and the psychological factors that affect daily functioning. Through CureOnCall, she contributes to patient-friendly mental health content that explains complex psychological concerns in a clear, practical and supportive way.
