What causes infidelity in relationships?

The question of “what causes infidelity in relationships?” has intrigued researchers for decades. Research, published in the British Journal of Psychology, claims that poor impulse control may be a significant factor with many unfaithful young partners. However, it’s not very convincing.

It’s becoming clear that both personal history and personality disorders are important factors that contribute to poor impulse control and infidelity in relationships. But neuroscience suggests that low serotonin levels in the brain may also play a role.

Impulse control problems are a compelling mental health issue in many difficult couples therapy cases. It’s estimated that about 9% or more of the general population struggles with an ICD (impulse control disorder).

Some researchers suggest that this number is actually higher.

ICD’s are frequently underdiagnosed, partially because insurance companies refuse to cover treatment for them. Couples therapists are seeing more cases involving behavioral addictions, such as the compulsive use of porn, as well as a rising rate of marital infidelity.

An ever-growing number of people today are being diagnosed with attention-deficit disorder, hyperactivity disorders, as well as various kinds of addictions.

Many different mental health issues such as Bi-Polar Disorder and Developmental Trauma have also been correlated with poor impulse control and compulsive sexual acting out, sometimes leading to infidelity.

Impulsive spouses tend to act on their immediate thoughts, feelings, and desires without considering the consequences.

We seem to be living in an age where self-discipline and self-regulation are the quaint artifacts of a simpler time. Some thought-leaders have speculated that technology is aggravating ICD’s by bestowed instant gratification upon us as a cultural norm, but brain science may point to dietary changes resulting in lower levels of serotonin as contributing factors as well.

What causes infidelity in relationships? Research on the role of poor impulse control

The Queensland study conducted a survey of 123 heterosexual people who were age 17 to 25 All of the study subjects were currently in a relationship. One obvious problem in generalizing the findings of this study was the discussion of poor impulse control in a population of study subjects whose brains may not have fully myelinated.

In other words, impulse control is an all-too-common problem in the 17 to 25-year-old age bracket. I agree that there is anecdotal evidence that impulse control may be an emerging problem in the more mature couple population that pursue couples therapy. But clearly, better research on ICD, and how it impacts marriages over a long period is needed.

This study, because of a narrow focus on young adults, offers suggestive, but unconvincing evidence of the role that poor impulse control might play in infidelity in an older population.

The question of the role of poor impulse control is interesting, but this particular study isn’t going to be of much help, in my opinion.  Most young adults between the age of 17 to 25 do not yet have fully mature, adult brains.

Asking about poor impulse control among young adults is like asking why fish swim.

Neuroscience and impulse control

Neuroscience is having an incredible impact on mental health. For example, impulse control issues routinely present in couples therapy. These are often serious, trust-eroding behaviors resulting in “last-shot”couples therapy.

Neuroscience research indicates that low serotonin levels in the brain may erode impulse control.

For example, recent research showed that reducing serotonin levels with a tryptophan-restricted diet results in more impulsive decisions. Other research (Bevilacqua, 2010) found that a mutation in the serotonin 2B receptor rendered a subset of the Finnish population to severe impulsivity.

We also know that Lithium may reduce impulsivity. One animal study found that a “moderate” dose of lithium (20 mg/kg) suppressed impulsive behavior (Ohmura, 2012). Research involving low concentrations of lithium found naturally in mineral waters and in some tap water has reportedly reduced impulsiveness and suicidality in the partaking population.

This research suggests a useful, inexpensive, over-the-counter way to reduce impulsivity. Ask your doctor if taking a lithium or tryptophan supplement is right for you.

Trytophan helps increase serotonin levels in the brain, and lithium is a known mood-stabilizer. This is the kind of data that a good, science-based couples therapist will bring to their clients on a routine basis.

What causes infidelity in relationships? Is it impulse control disorders?

Research shows that people who cheat on their partners don’t tend to dwell on their impulse control issues. Instead, low relationship satisfaction, especially for women, as well as a sense of disconnection, are typically offered as explanations for their unfaithful behavior.

As expected, the availability of an “attractive other” is also a significant catalyst for what causes infidelity in relationships. The availability of a willing “attractive other” brings us back to the issue of poor impulse control. The University of Queensland study also claimed that relationship duration and even the degree of commitment were not factors that impacted infidelity.

What causes infidelity in relationships? The upside of experiencing an unfaithful spouse

It’s funny how the words we use change over time. Today we talk about “impulse control.” In yesteryear, we called it “good character.”

A recent cross-cultural study explored the implications of infidelity for the women on the receiving end.

This research didn’t ask “what causes infidelity in relationships?” Instead, it asked, “what happens to the hurt partner, the involved partner, and the affair partner after the infidelity broke up the relationship?”

It was an impressive survey of nearly 6000 partners from almost 100 countries. This was a sizeable cross-cultural study, and the findings were fascinating. There has been a huge amount of research on couples struggling to stay together after infidelity.

I like the fact that this study focused on relationships that ended over infidelity. It’s important to note that in the USA, most couples that want to recover from infidelity manage to do that with good couples therapy.

Discovering that your partner has been unfaithful is severe and painful trauma, but this research suggests that women who have been cheated on may actually go on to have better and more successful intimate lives with their next partner. It’s another example of how intuition can be shaped by trauma.

Post-traumatic growth of the hurt partner

This research shows that women who lose a relationship because of infidelity may experience post-traumatic growth.

It takes a little time, but these women develop more self-confidence and self-awareness. And they eventually bond with more reliable men with better self-control.

The ultimate loser is the mate poacher, now saddled with an unreliable partner with poor impulse control. The “other woman” quickly learns that he wasn’t such a great catch after all. Dr. Craig Morris, one of the principal authors of this research:

“The woman who ‘loses’ her mate to another woman will go through a period of post-relationship grief and betrayal, but come out of the experience with higher mating intelligence that allows her to better detect cues in future mates that may indicate low mate value. Hence, in the long-term, she ‘wins.’”

“Most women who have lost a mate to another woman report a ‘silver lining’ of higher mating intelligence. What this means, in their words, is that they are more attuned to cues of infidelity in a future mate, more aware of how other women interact with their mate, have more self-confidence and more self-awareness, and independence in general.”

Do mate poachers get the booby prize?

Essentially, many different women who were cheated on are less likely to be fooled again.

They have learned to spot potentially unfaithful men, and no longer feel vulnerable to getting involved with them.

The study reports that often as soon as six months to a year later, women who experienced infidelity developed a higher degree of emotional intelligence.

And what of the mate-poacher?

Researchers also found that in the majority of cases, the unfaithful partner’s new relationship soon blows up.

After the previous relationship breaks up, relationships with affair partners are incredibly unstable. Evidence from this study indicates that a woman who poached a partner from another woman will typically fail to enjoy a successful long-term relationship with her new partner.

Is poor impulse control what causes infidelity in relationships? Maybe in some cases, but certainly not in all.

We still don’t know what causes infidelity in relationships

While the first study suggests that poor impulse control might be a factor in infidelity, the researchers committed a fundamental error by using young adults as study subjects.

However, the research on hurt partners had a much better design. Unfortunately, that study told us more about women leaving unfaithful partners than it told us about what causes infidelity in relationships.

There are some things we do know. If an affair ultimately results in marriage, (and only a fraction ever do), research tells us that 75% of them end in divorce within 5 years.

Bit what is true is that when a new relationship forms between affair partners, establishing trust in a new committed relationship between former affair partners can be a difficult uphill struggle.

Are you wanting to recover from infidelity in your relationship?


Bevilacqua et al. A population-specific HTR2B stop codon predisposed to severe impulsivity. Nature. 468:1061-6 (2010).

Ohmura et al. Lithium, but not valproic acid or carbamazepine, suppresses impulsive-like action in rats. Psychopharmacology. 219:421-32 (2012).

Originally published August 19, 2018.

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Daniel Dashnaw

Daniel is a Marriage and Family Therapist and the blog editor. He currently works with couples online and in person. He uses EFT, Gottman Method, Solution-focused and Developmental Models in his approaches. Daniel specializes in working with neurodiverse couples, couples that are recovering from an affair, and couples struggling with conflict avoidant and passive aggressive behavior patterns.

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