Are you ever around women who seem frustrated, upset or irritated? Have you ever asked one of them if she was on her period or perhaps been tempted to inquire?

Take it from me: Don’t. Presuming that female reproductive organs make women behave irrationally is rude and sexist. It also evokes the same unscientific beliefs that have always held women back.

I’m a sociologist who researches the perils women experience on a daily basis simply for existing. In studying the systemic nature of sexism, I’ve learned that men and women alike can contribute to gender inequality in seemingly innocuous ways, including through what might seem like small talk.

Hysteria and menstrual taboos

One big problem with asking about periods has to do with the underlying assumptions behind that question. The same person who might want to find out if there’s a legitimate reason for their male colleague to become angry, frustrated or agitated might ascribe those same reactions in a woman to menstruation.

All women are subjected to this assumption regardless of whether they actually have the capability to menstruate or don’t for whatever reason, including menopause and being transgender. This double standard rests on assumptions of female biological inferiority and reinforces a prejudice stretching back to ancient times.

For most of history, women in many cultures were denied equal access to public spaces and career opportunities for one reason: having a uterus.

Female reproductive organs supposedly rendered women too “hysterical” – an English term derived from the Greek word “hysterika,” meaning uterus – to rule, learn or give any sort of valuable input. Although the symptoms of hysteria changed throughout cultural contexts, symptoms were consistently connected to the prevailing medical beliefs of women’s biological anatomy.

The ancient Greeks believed women were hysterical because they had “roaming uteruses” that moved around within their bodies. In the Victorian era, the British referred to it as a “nervous-weakness” or “faintness” – never mind that women were expected to wear tight corsets that made it hard to breathe. Regardless, the men diagnosing hysteria used it to justify keeping women at home and out of the public realm.

Throughout time and in most cultures, labeling women as “hysterical” continued to suggest that women’s competence, or lack thereof, remained anchored to their reproductive organs. And since men don’t have periods – with rare exceptions – they seemed to be more rational and reliable.

Not moving on

Research suggests that millennials and members of Generation Z – Americans born between 1995 and 2015 – are more accepting of people regardless of their sexual orientation or gender identity than earlier generations. Despite that, I’ve found that sexism remains a daunting problem for young adults.

I spent three years conducting a study involving roughly 185 college students attending two large universities in different parts of the country. The majority were women, and two-thirds were white. I asked the participants, who were between 18-21 years old, to write down anything they perceived, witnessed, experienced or observed to be examples of sexism for six weeks.

I’m still analyzing this data, which I collected for my dissertation and will use for multiple projects that are still underway.

Female participants recounted many experiences, including being catcalled as well as being given secretarial positions in STEM group projects because their male group members didn’t believe they were smart. A total of 12 women recounted being asked whether they were having periods, usually by men.

Men without filters

One student I’ll call “Stephanie” to protect her privacy described what happened while she was studying with other students. After becoming frustrated doing math homework because she kept getting the wrong answer, she shut her computer and angrily told the members of her study group she needed a break. Matt, the only man present, asked her if she was on her period.

While on their way to a nearby neighborhood to sled, “Jamal” flirted with “Candice,” but his “charms” went unreciprocated. Jamal told the two other women present that it was “probably because she was about to start her period cycle.”

These incidents can happen anywhere. I found an example involving this question in the workplace, and I also personally experienced it while working as an IT recruiter several years ago when my boss once asked if I was feeling OK. Upon hearing “I’m fine, just tired,” he mouthed, “Are you on your period?” while nodding in an understanding, sympathetic way.

What to expect when you’re around a woman

The subtext for this kind of everyday sexism was clear to many of the women in my study: Society expects women to be cheerful unless nature intervenes.

“Anytime a woman is slightly in a bad mood, it’s always because we’re on our period,” said “Ashley” sarcastically, adding, “All other times we should be in the best mood, always smiling, and happy.”

Not every enforcer of this social norm is male. Two of the women in my study noted that other women asked them that same question. They recalled being equally offended. Unlike what happened when men asked this question, however, they immediately objected, saying it was sexist.

The word “hysteria” might mean something different today than it used to. But the notion that women are not as competent and capable as men in math, engineering and other male-dominated fields persists. Commonly held sexist beliefs blame women’s lower status on biological differences between genders. In my view, this prejudice hinders women on many career paths, including politics and the law, contributing to the gap between what women and men earn for comparable work.

Therefore, unless you actually believe in women’s inferiority and want to imply that you don’t think women and girls can act rationally, never ever ask them at any point in time, “Are you on your period?”

Melissa K. Ochoa does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.