The biology of relational infidelity

Are men with high testosterone levels more likely to cheat?

Source: Image by MARIO OLAYA from Pixabay

In the film Unfaithful, which many consider the gold standard in films about infidelity, Diane Lane’s character seems to have it all: a lovely house, kids, and a handsome, if somewhat boring, husband (Richard Gere). However, she is unfaithful after a chance encounter with an attractive younger man (Olivier Martinez). Why should she risk the stability of her reasonably happy marriage by cheating?

There are many reasons why people would risk their relationship by committing infidelity. It could be something about the cheater (his personality or self-esteem), something about the relationship (unsatisfactory or unfulfilled), or something about the situation (the person just got the chance). However, there could also be biological and hormonal factors that at least partially influence fraud behavior. (See this video for “The Science of Cheating”)


Research has found a relationship between relationship status and testosterone levels in men (Burnham et al., 2003). Men who were in a committed romantic relationship, in particular, had testosterone levels that were 21% lower than men who were single. Similarly, a separate study found that men with higher testosterone levels had a greater interest in sex outside of their relationship, which, provided their partner does not tolerate it, is essentially cheating (McIntyre et al., 2006).

In a 2019 study, researchers took saliva samples from 225 middle-aged European men and asked if they had remained true to their current relationship (Klimas et al., 2019). In the sample, 37.5% of the men said they had cheated. The researchers also found that those who committed infidelity were also more likely to have higher testosterone levels than 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).

With these findings in mind, you may now be wondering about your current partner’s hormone levels. While it may be tempting to secretly use a test kit to find a partner’s testosterone and estrogen levels, we don’t have to worry about all of these issues. There is a much easier way to find out about hormone levels. As? By listening to the voices of our partners (O’Connor, Re & Feinberg, 2011). Men with lower voices (e.g. Barry White, George Clooney, Morgan Freeman, and others) have higher levels of testosterone, while women with higher voices (e.g. Taylor Swift or Katy Perry) have more estrogen. If the pitch of the voice is related to hormone levels, it may also be related to cheating.

It seems that we intuitively associate infidelity and pitch. In one study, participants heard audio clips of male and female voices that were digitally altered to achieve a higher or lower pitch. The participants then used their votes to indicate how likely it is that each person would cheat. The results showed that participants considered men with low male voices and women with high female voices to be more deceitful than high voices men or low voices women. Although deep male voices tend to be more attractive, when women want a long-term relationship they avoid deep male voices due to the man’s perceived potential for cheating (O’Connor et al., 2014). In contrast, in short-term relationships, where cheating is less of a problem, women preferred men with more masculine voices.

Ovulatory cycle

In women, their ovulatory cycle is another biological factor that can affect their chances of cheating (Pillsworth & Haselton, 2006). In particular, women are more likely to cheat when they are most likely to become pregnant (i.e. when they are ovulating). Whoa: That seems like an absolutely terrible idea. Why should that be so? From an evolutionary point of view, women should have a desire to preserve the best possible genes (think Channing Tatum, Jason Derulo, or Zack Efron) for their offspring. But such a sexy partner may not stick with raising the child, so she needs to have a more stable partner who provides security (think Phil of Modern Family) – which is why a woman may choose to cheat rather than her primary partner to leave altogether. Therefore, if a woman is in a relationship with a partner of inferior quality (think Napoleon Dynamite) she is cheating when she is most fertile so that her offspring have the benefit of better genes. The hope here, of course, would be that old Napoleon wouldn’t find out.

These biological influences could make it sound like a person can’t help but cheat because they are at the mercy of their hormones. However, it is Not what research shows. If biology were fate, every high testosterone man and every high estrogen woman would be a serial cheater, which is clearly not the case. Hormones can make resistance more difficult, but people have the ability to be self-aware and self-reflective and should therefore be held accountable for their own decisions.

Interested in what kind of person is more cheated on? Click here.

To learn more about the psychology of relationships, check out my new book Stronger Than You Think: The 10 Blind Spots That Undermine Your Relationship … And How To Look Past Them. You can also follow me on Twitter.

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