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The Biology of Relationship Infidelity

How hormones may influence whether our partner cheats.

Are men with high testosterone more likely to cheat?
Source: Image by MARIO OLAYA from Pixabay

In the movie Unfaithful, which many consider the gold standard among films about infidelity, Diane Lane’s character seems to have it all: a nice house, kids, and a hunky, albeit slightly boring, husband (Richard Gere). Yet, following a chance encounter with an attractive younger man (Olivier Martinez), she finds herself being, well, unfaithful. Why would she risk the stability in her reasonably happy marriage by cheating?

There are lots of reasons why people would risk their relationship by committing infidelity. It could be something about the cheater (their personality or self-esteem), something about the relationship (not satisfying or unfulfilling), or something about the situation (the person just had the chance). However, there could also be underlying biological and hormonal factors that, at least partially, influence cheating behavior. (See this video on "The Science of Cheating")


Research has identified a link between relationship status and men’s testosterone levels (Burnham et al., 2003). Specifically, men who were in a committed romantic relationship had testosterone levels that were 21% lower than men who were single. Similarly, a separate study found that men who had higher testosterone levels reported more interest in having sex outside of their relationships, which, assuming his partner does not condone, is essentially cheating (McIntyre et al., 2006).

In a 2019 study, researchers took saliva samples from 225 middle-aged European men and also asked about whether they had been faithful in their current relationship (Klimas et al., 2019). In the sample, 37.5% of the men reported that they had cheated. Researchers also found that those who had committed infidelity were also more likely to have higher testosterone levels compared to those who did not report cheating. These types of effects aren’t just limited to men: Research also suggests that women with higher levels of estrogen may be more likely to cheat (Durante & Li, 2009).

Now, in light of these findings you may wonder about your current partner’s hormone levels. Though it may be tempting to surreptitiously use a testing kit to detect a partner’s testosterone and estrogen levels, we don’t need to go to all that trouble; there’s a much easier way to detect hormone levels. How? By listening to our partners’ voices (O’Connor, Re, & Feinberg, 2011). Men with deeper voices (e.g., Barry White, George Clooney, Morgan Freeman, and others) have higher testosterone levels, while women with higher voices (e.g., Taylor Swift or Katy Perry) have more estrogen. If voice pitch relates to hormone levels, it may link to cheating as well.

It seems we intuitively link infidelity and voice pitch. In one study, participants listened to audio clips of male and female voices that had been digitally altered to be higher or lower in pitch. Based on their voice, participants then indicated how likely each person would be to cheat. The results revealed that participants considered men with masculine deep voices and females with feminine high voices as more likely to cheat than men with high voices, or women with deep voices. Although deep male voices are typically more attractive, when women desire a long-term relationship, they tend to avoid the low-pitched male voices because of the male’s perceived potential for cheating (O’Connor et al., 2014). In contrast, when considering short-term relationships where cheating is less of a concern, women preferred men with more masculine voices.

Ovulatory Cycle

For women, their ovulatory cycle in another biological factor that may influence her likelihood of cheating (Pillsworth & Haselton, 2006). Specifically, women are more likely to cheat when they are most likely to get pregnant (i.e., when they are ovulating). Whoa: This seems like an absolutely terrible idea, so why would this be? Evolutionarily speaking, women should desire to obtain the best genes possible (think Channing Tatum, Jason Derulo, or Zack Efron) for their offspring. But such a sexy mate may not stick around to raise the child, so she needs to have a more stable partner who will provide security (think Phil from Modern Family)—which is why a woman may decide to cheat rather than abandoning her primary partner altogether. As a result, if a woman finds herself in a relationship with a lesser quality partner (think Napoleon Dynamite), she’ll cheat when she is most fertile so that her offspring will have the benefit of better genes. Of course, the hope here would be that old Napoleon wouldn’t figure it out.

These biological influences might make it sound like a person can’t help cheating because he or she is at the mercy of their hormones. However, that is not what the research shows. If biology were destiny, then every high-testosterone male and high-estrogen female would be a serial cheater, which clearly isn’t the case. Rather, hormones may make resisting harder, but people have the ability to be self-aware and self-reflective and thus should be held accountable for their own choices.

Interested in what type of person gets cheated on more? Click here.

To learn more about the psychology of relationships, see my new book Stronger Than You Think: The 10 Blind Spots That Undermine Your Relationship...and How to See Past Them. You can also follow me on Twitter.

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Burnham, T. C., Chapman, J. F., Gray, P. B., McIntyre, M. H., Lipson, S. F., & Ellison, P. T. (2003). Men in committed, romantic relationships have lower testosterone. Hormones and Behavior, 44(2), 119–122.

Durante, K. M., and Li, N. P. (2009). Oestradiol level and opportunistic mating in women. Biology Letters, 5, 179-182.

Klimas, C., Ehlert, U., Lacker, T. J., Waldvogel, P., & Walther, A. (2019). Higher testosterone levels are associated with unfaithful behavior in men. Biological Psychology, 146.

McIntyre, M., Gangestad, S. W., Gray, P. B., Chapman, J., Burnham, T. C., O’Rourke, M. T., & Thornhill, R. (2006). Romantic involvement often reduces men’s testosterone levels–but not always: The moderating role of extrapair sexual interest. Journal of Personality and Social Psychology, 91(4), 642-651.

O’Connor, J., Re, D., & Feinberg, D. (2011). Voice pitch influences perceptions of sexual infidelity. Evolutionary Psychology, 9, 64-78.

O’Connor, J. J. M., Pisanski, K., Tigue, C. C., Fraccaro, P. J., & Feinberg, D. R. (2014). Perceptions of infidelity risk predict women’s preferences for low male voice pitch in short-term over long-term relationship contexts. Personality and Individual Differences, 56, 73–77.

Pillsworth, E. G., & Haselton, M. G. (2006). Male sexual attractiveness predicts differential ovulatory shifts in female extra-pair attraction and male mate retention. Evolution and Human Behavior, 27(4), 247-258.

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