Men and women lie about their sexual histories, but only when they think they won't get caught in the act, according to new research published in the journal Sex Roles.

Ohio State University researchers hooked up 293 college students to polygraph machines and asked them about a range of stereotypical “male” and “female” behaviors. The students were honest about most of their deeds, from telling obscene jokes to singing in the shower, but lied through their teeth about their sexual experience in order to live up to social expectations of sexuality.

The students were given a 124-point questionnaire about various behaviors that had been independently rated as “masculine” or “feminine,” such as wearing dirty clothes (masculine) verses writing poetry (feminine). Half were hooked up to the lie detector before answering the questions, and the other half were connected to the machine while filling out the questionnaire.

The polygraph wasn’t functional, but the students believed they were really being monitored. They admitted to everything from making fun of others to lying about their weight, but when asked about whether they had ever had sex and their number of sexual partners, men who weren’t attached to the lie detector exaggerated their experience while women downplayed it.

"There is something unique about sexuality that led people to care more about matching the stereotypes for their gender," Terri Fisher, study author and professor of psychology at Ohio State University, said in a press release. "Sexuality seemed to be the one area where people felt some concern if they didn't meet the stereotypes of a typical man or a typical woman."

This kind of gender-based sexual posturing may seem harmless, but lying to your doctors or sexual partners about your past—and being lied to, for that matter—could increase your risk of contracting and spreading a sexually transmitted infection (STI).

Previous studies have shown that young people, especially men, sometimes lie about their sexual history and STI risk factors. With 20 million new STI diagnoses every year—half among young people ages 15 to 24—nondisclosure is a cause for concern.

Times, They Are a-Changin’

Fisher conducted a similar experiment back in 2003 and found that women reported having fewer sexual partners when not hooked up to a lie detector, but said they’d had about the same number of partners as their male counterparts when hooked up to the machine.

In the 2013 experiment, when both groups were hooked up to a polygraph, women in fact reported having more sexual partners than men. Fisher concludes that though gender stereotypes—and the pressure to live up to them—still exist in the U.S., women now feel more at liberty to express their sexuality.

"Society has changed, even in the past 10 years, and a variety of researchers have found that differences between men and women in some areas of sexual behavior have essentially disappeared," she said.

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