Men who cheat on their romantic partner tend to also have higher testosterone levels than men who don’t cheat, according to new research published in the journal Biological Psychology.

“We were interested in the topic because there are still too few reliable findings regarding the potential relationship between infidelity and testosterone. Especially in men without sexual dysfunction, this relationship had not yet been sufficiently investigated,” said study co-author Andreas Walther, a postdoctoral researcher at Technichse Universität Dresden.

For their study, the researchers surveyed 224 middle-aged men who were currently in a relationship. The participants completed online surveys to assess their sexual functioning, infidelity, and other variables. About one week later, the participants visited a laboratory to have their testosterone levels measured.

The researchers found that about 37% of the men admitted to having been unfaithful in their current relationship one or more times. The men’s testosterone levels were also associated with their unfaithful behavior.

“The main message is that testosterone is associated with infidelity and that higher testosterone concentrations appear to be associated with a higher probability of being unfaithful,” Walther told PsyPost.

“In addition to testosterone, factors such as sexual function, relationship quality, alcohol consumption, depressivity had been investigated, and in addition to testosterone, increased alcohol consumption was consistently associated with a higher probability of being unfaithful.”

But the study — like all research — includes some caveats.

“The major limitation of the study is that it is not an experimental study that could prove with testosterone administration, for example, that those men with testosterone administration are significantly more often unfaithful compared to men receiving a placebo. Such a study is unfortunately very difficult to conduct due to the obvious obstacles to feasibility,” Walther explained.

“A question still open is whether this relationship between higher testosterone concentrations and a higher probability of being unfaithful can also be demonstrated in women. We know that testosterone administration has similar effects in different dimensions in women as it does in men (e.g. mood, sexuality) and would therefore hypothesize that it is similar. However, there are no reliable data on this.”

Previous research had found that young men in committed relationships tended to have lower testosterone levels compared to young men who were single. But men in relationships who reported cheating on their partners tended to have testosterone levels that were about as high as single men.

Testosterone, of course, is not the only factor that influences cheating behavior.

“It is important to note that higher testosterone levels are not a deterministic factor that necessarily leads to infidelity, but only increases the probability,” Walther said.

“It is also important to note that the effect sizes (the strength of the associations) are moderate and such a complex behaviour as infidelity is determined by numerous factors of which the testosterone concentration is only one.​”

The study, “Higher testosterone levels are associated with unfaithful behavior in men“, was authored by C. Klimas, U. Ehlert, T.J. Lacker, P. Waldvogel, and A. Walther.