Many men take great pride in the above-average size of their penises, believing that this physical gift is the key to bringing sexual satisfaction to their female partners. A new study conducted by a team of researchers from the U.S. and Kenya found that men boasting larger penises might want to think twice: Every one inch longer in penis length increased the likelihood of a wife’s infidelity by almost one-and-half times. “Women associated large penises with pain and discomfort during sex which precludes the enjoyment and sexual satisfaction that women are supposed to feel,” wrote the authors of this new research. Their report appears in PLoS ONE.

The Marriage Bed

Despite many negative consequences caused by infidelity, the behavior is reported around the world in many if not every culture. Reports of extra-marital affairs range from 30 to 60 percent among men and 20 to 50 percent among women, according to some research. Yet for some, the consequences of infidelity may include heart problems or even cardiac arrest brought on by all the psychological stress involved in sneaking around and the "excitement" of the actual if brief encounters. What makes infidelity thrilling also makes it deadly. Even in cases where it is simply suspected, infidelity also gives rise to depression, domestic violence, and in some extreme cases, spousal homicide. Most obviously, extra-marital affairs cause separations, which is also bad for your health, with up to 50 percent of all divorces in developed countries caused by concerns of infidelity.

Marriage is also believed to be a risk factor for STDs and HIV infection. Because the marriage bed usually does not require using a condom, when a partner strays and contracts a sexually transmitted disease, the spouse easily gets it as well. Women’s involvement in partnerships outside of marriage is critical, then, in predicting HIV infections and for this reason, a team of researchers from Kenya and the U.S. decided to investigate the reasons why women would cheat.

To conduct this study, the research team focused on fishermen and their wives, conducting a total of 1,090 interviews with 545 married couples between the ages of 18 and 45 from 33 beaches in Kenya. The interview covered a number of topics, including socio-economic and demographic details, marital and sexual relationships and number of sexual partners in six months preceding the study. Over 90 percent of the women were in a monogamous marriage, their median age was 24, (the median age at first marriage was 18), and a quarter reported their sexual debut occurring before the age of 13.

Overall, 6.2 percent of the women told the researchers that they had been unfaithful to their husbands during the preceding six months, while more than a quarer (27 percent) suspected their husbands of being involved in extra-marital relationships. Probably the team’s least surprising discovery, then, was that the strongest predictor of a woman straying from her marriage bed was a suspicion that her spouse was involved with someone else.

Unsurprisingly, domestic violence also contributed to the likelihood of a woman becoming unfaithful to her husband as did lack of womanly satisfaction. In particular, being denied a preferred sex position and a spouse’s longer penis inspired some of the wives to wander. “Our results show that in the perspective of women, large-sized penises are associated with extra-marital partnerships possibly due to pain and discomfort during sex,” wrote the authors. “This is contrary to men's perspectives … [due to] the received and popularized fallacy equating a larger penis size with masculinity.”

Conversely, a woman's older age and higher satisfaction scores reduced the likelihood of a wife reporting extra-marital partnerships. Women older than 25 were 28 percent less likely to cheat when compared to younger women and for each one unit increase on the sexual satisfaction scale, the chances of a wife's infidelity lessened by a whopping 92 percent. Ultimately, then, the researchers found that satisfaction in marriage is key to a woman remaining faithful to her husband while also verifying all of men’s suspicions that penis size does matter to women. The one thing is it just happens to matter in an opposite way than men commonly believe.

Source: Kwenamail Z, Mwanzo I, Shisanya C, Camlin C, Turan J, Achiro L, Bukusi E. Predictors of Extra-Marital Partnerships among Women Married to Fishermen along Lake Victoria in Kisumu County, Kenya. PLoS ONE. 2014.