For Years, Western Scientists Stigmatized Periods. We’re Living the Consequences.

“All that mythologizing really got in the way of proper science being done.”

— Elinor Cleghorn, the author of “Unwell Women: Misdiagnosis and Myth in a Man-Made World.”

[In Her Words is available as a newsletter. Sign up here to get it delivered to your inbox.]

It was obvious, the esteemed physician explained, why women could not safely pursue education and a career outside the home.

The reason was awful to think about and even worse to state, but the British psychiatrist Henry Maudsley was going to speak the truth as directly as a Victorian gentleman could:

Comparing men and women was “not a question of two bodies and minds that are in equal physical conditions, but of one body and mind capable of sustained and regular hard labor, and of another body and mind which for one quarter of each month during the best years of life is more or less sick and unfit for hard work,” he wrote in an influential 1874 article in Popular Science Monthly. “The gravity of the subject can hardly be exaggerated.”

In other words: Women menstruated.

The very act, according to Dr. Maudsley, diminished women’s strength, immune function and cognitive ability. Women risked disaster by exerting themselves further through work or study.

Dr. Maudsley didn’t need to use data or case studies to make his point. He was referencing a widely held theory in medicine then that the menstrual period was a time of weakness and ill health. Often referred to at the time as “functional periodicity,” this quasi-scientific term gave the theory an air of medical legitimacy and armed opponents of women’s education, careers and suffrage.

“The easiest way for anti-feminist and misogynistic doctors to marshal arguments against the expansion of women’s rights was to essentially say, well, they are all sick for at least a week a month,” said Elinor Cleghorn, the author of the recent book “Unwell Women: Misdiagnosis and Myth in a Man-Made World.”

In the absence of scientific understanding about the process of menstruation, Western doctors ascribed their patients’ symptoms to their behavior. Women could trigger their periods early by indulging in “a long visit to cities,” one physician wrote in 1891, or “a diet of exciting foods.”

In his 1851 book “On Diseases of Menstruation and Ovarian Inflammation,” Dr. Edward John Tilt explained that women could “overexcite” their reproductive organs through the “prurient incitement of passion-stirring pictures, statues, music, novels, and theatres.”

When the London Obstetrical Society voted in 1873 to bar women doctors from joining its ranks, Dr. Tilt — then the organization’s president — praised the decision on the basis that women were not “qualified by nature … to bear the physical fatigue and mental anxieties of obstetrical practice at menstrual periods.”

As Dr. Cleghorn points out in her book, pathologizing menstruation gave doctors a pass to dismiss the complaints of women suffering from painful disorders like endometriosis or fibroids. Excessive bleeding or agonizing cramps were just part of the package of “women’s troubles,” an umbrella diagnosis for which the only reliable cure was rest — and, of course, the avoidance of taxing activities like study, work or politics.

The way out of this pseudoscientific prison was through data-driven science.

In response to a well-publicized lecture from a Boston physician who warned that rigorous study could harm women’s fertility, the New York physician Mary Putnam Jacobi published in 1877 a study of 268 women from various backgrounds. The majority of her research subjects did not require bed rest during menstruation, and those who reported extreme pain during their periods often suffered from an underlying condition. Her remarkable conclusion — that a menstruating body was not a sick one — earned her the prestigious Boylston Medical Prize, the first time the honor was awarded to a woman.

As an undergraduate in the 1890s, Clelia Duel Mosher conducted her own investigation into the validity of functional periodicity, interviewing fellow students about their menstrual cycles. She analyzed the data a few years later as a medical student at Johns Hopkins, and found no evidence that menstruation incapacitated all women — in fact, women who were more physically active were less likely to report pain during their periods.

“A new and more limited view of menstruation must come,” she wrote in 1911. “In the emphasis and exaggeration of this one expression of the sexual activity of women, her efficiency has been lessened and we have lost sight of the common biological basis of life.”

Today, of course, it’s no longer professionally plausible for a doctor to argue that all women are physically incapacitated during their periods. But because Western scientists for so long stigmatized menstruation, and excluded input from female physicians who might have been more willing to study periods and other functions of female biology, science got a late start collecting quality data on menstruation.

Even today there remains what the author Maya Dusenbery calls a “knowledge gap” between what doctors know about women’s bodies and the comparatively greater amount they know about men’s. People who have periods end up suffering for it.

Take, for example, the number of women who have reported disruptions to their menstrual cycles after getting the coronavirus vaccine. While there’s no formal data linking the vaccine to menstrual issues, clinical trials in the U.S. aren’t required to gather information on changes in menstrual cycles as a side effect — so most don’t, and an opportunity to better understand the vaccine’s potential effects on roughly half the population is lost.

Simply put: “Menstruation is something we don’t know enough about,” Dr. Hugh Taylor, chair of the department of obstetrics, gynecology and reproductive sciences at Yale School of Medicine, told the authors of a recent Times op-ed on the subject. “It’s an important indicator of a person’s health, like any other bodily function.”

For Dr. Cleghorn, the path that led us here is clear.

“You can chart the lack of understanding that we’ve inherited now back to the ignorance around women’s blood and pain and the mythologizing of women’s blood and pain,” she said. “All that mythologizing really got in the way of proper science being done.”

In Her Words is available as a newsletter. Sign up here to get it delivered to your inbox. Write to us at inherwords@nytimes.com.