This article is a preview from the Summer 2017 edition of New Humanist. You can find out more and subscribe here.

Few people suffer from debilitating pain without anyone knowing about it. Yet I have, and I do. There’s a small ridge along my scalp which traces the stitches I received as a teenager when I passed out from period pain, hitting my head on the hard stone floor of the school’s physics laboratory. My monthly pain can still curl me into a ball, although these days I manage it well with delicately timed doses of ibuprofen. I do this quietly, without anyone knowing. And I maintain this silence because, of course, that’s how society prefers its menstruating women. Faces flush at the mere sight of a tampon. Nobody wants to be the one to tell the girl about the red stain on the back of her dress.

This culture of shame and embarrassment, though, may now be lifting. After thousands of years of being thickly lacquered in euphemism, we’re finally becoming free to talk about periods. The ancient menstrual taboo is being powerfully challenged by women all across the world.

In June 2016 sanitary towel brand Bodyform broke with advertising industry convention by using actual blood, not blue liquid, in their commercials. “No blood should hold us back,” proclaimed the strapline. Adverts for sanitary towels had until then oddly skirted around what they’re actually designed for. It was a small change, but an important one. Women’s health activists and NGOs have long highlighted the damage the menstrual taboo does to young women in the developing world who can’t access adequate sanitary protection and hygienic toilets. Some skip school as a result. Recently, it emerged that some girls in the UK miss school because they can’t afford tampons or pads.

What began as a marginal human rights issue has since broadened, transforming into a global movement demanding more openness about menstruation. At its heart is a simple question: why does mention of a woman’s period bother so many quite so much? Why can’t we be honest about something this mundane?

Historically, it’s hard to pin down when the menstrual taboo emerged. It’s certainly old enough to be enshrined in the major religions. “When a woman has her regular flow of blood, the impurity of her monthly period will last seven days, and anyone who touches her will be unclean till evening,” says Leviticus. Taking their cue from this passage, Orthodox Jews refer to a menstruating woman as “niddah”, meaning separated. She’s considered too impure to have sex as long as seven days after her period is over.

Were there practical benefits to the ancients of forcing women into isolation during their periods – for hygiene or medical reasons, or to allow women to rest? Perhaps. Other theories suggest that the taboo may have emerged to spare men their fear of menstrual blood. In many religions, a menstruating woman is not just cursed, she defiles others by her very presence. Menstruating women are advised by some not to partake of Holy Communion. Certain Islamic scholars say they shouldn’t enter a mosque or even pray.

Some academics have interpreted the menstrual taboo as a way to discriminate against women and enforce patriarchal control over their sexuality. Among the Dogon people of Mali, women who follow the traditional religion are expected to cloister themselves in menstrual huts during their periods. Research by anthropologist Beverly Strassman at the University of Michigan has shown that men may be using these huts to covertly track their wives’ fertility to ensure their children are really their own. What’s clear is that countless layers of shame and secrecy have been applied to periods over many centuries and that at least some of it is in the interests of men.

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Lifting the curse is now a feminist issue. In India, where the taboo is particularly entrenched, a woman on her period isn’t supposed to enter a Hindu temple. According to research into menstrual myths by Suneela Garg and Tanu Anand of Maulana Azad Medical College in New Delhi, the origins for this can be found in the Vedas, Hinduism’s ancient scriptures. The belief is that menstrual flow is the manifestation of guilt felt by the god Indra after killing Vritra, the demon of drought. “Further, in the Hindu faith, women are prohibited from participating in normal life while menstruating. She must be ‘purified’ before she is allowed to return to her family and day to day chores of her life,” write Garg and Anand. In rural areas, menstruating girls avoid kitchens because they’re thought too unclean to handle food.

This disgust with menstruation can have terrible consequences. In Nepal in December 2016, a 15-year-old girl died after being banished to a badly ventilated shed during her period. She was victim of an old Hindu tradition known as chhaupadi, practised in rural areas in the west of the country, which forces women into seclusion, often in cattle sheds alongside the animals.

But women are fighting back. In 2015 when one Hindu temple in the state of Kerala announced a blanket ban on all women of menstruating age, young Indians launched an angry campaign on social media. The #HappyToBleed hashtag was daubed on sanitary towels alongside #SmashPatriarchy and #BreakTheTaboo.

Across the world, menstrual activists are unashamedly displaying their bloodstained clothes on Instagram and campaigning against taxes on tampons and sanitary towels. Faced with the decision of whether to skip the 2015 London Marathon because she was on her period, 26-year-old Kiran Gandhi took the bold choice of not only running but allowing her blood to flow freely. “It is oppressive to make someone not talk about their own body,” she told Cosmopolitan magazine, which featured photographs of her after the marathon, her leggings stained. “I really can’t think of anything that’s the equivalent for men, and for this reason, I believe it’s a sexist situation.”

The following summer, Chinese Olympic swimmer Fu Yuanhui admitted to state broadcaster CCTV that she hadn’t performed at her peak in one race because she was on her period. Her honesty won global support. It followed a decision by some Chinese provinces to allow women time off work for severe period pain, joining other countries in the region that already do this, including Japan and South Korea.

This unparalleled frankness has also helped confront misogynistic stereotypes about how women behave when they’re on their periods. Which woman hasn’t been hurled the insult that her strong views might be the effects of pre-menstrual tension?

When Donald Trump told American television audiences that Fox News host Megyn Kelly had “blood coming out of her wherever” during a Republican debate she was hosting during his bid for the Presidency, the internet erupted in a firestorm of anger (he clarified his comment later by claiming he meant her nose, not her vagina). American artist Sarah Levy took to her paintbrush, rendering Trump’s angry face mid-speech in her own menstrual blood.

Where society leads, business often follows. For the multi-billion-pound tampon and towel industry, this shift in attitudes marks a sea change in how products can be marketed. It’s not just large brands like Bodyform taking advantage. The entrepreneurs behind THINX – which claims to be the world’s first period-proof underwear – affirm that their business is a political endeavour. “I want to be the taboo queen for the nether regions,” co-founder Miki Agrawal told Business Insider magazine. The company blog talks openly about periods as you might expect, but also about Gloria Steinem and wage equality.

Improving sanitary protection has transcended from being a matter of a woman’s comfort and hygiene to one of power and equality. It’s easy to be cynical when feminism gets exploited by business, but in this case the products available to women really are improving. Menstrual cups, tampons and pads have been revamped, and in some cases given glamorous makeovers. With these new products, the embarrassment around periods recedes even further.

At the same time, different versions of low-cost sanitary protection have been developed in India and Uganda to better meet the needs of women who otherwise resort to using rags, newspapers or ashes. In China last year, a company began work on the country’s first domestic tampon brand. Cracking through the menstrual taboo has had the practical effect of directly improving how women live.

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As for period pain, this too is getting some long-awaited attention from medical researchers. The silent relegation of menstruation to the margins for most of history rendered it one of the least understood medical issues. Even now, science has a fairly weak understanding of why women suffer period pain and pre-menstrual tension, and even fewer answers for how to manage it. A professor of reproductive health at University College London, John Guillebaud, told reporters at online magazine Quartz in 2016 that cramps can be almost as painful as having a heart attack. Yet, by his own admission, medics have failed to give the problem the prominence it deserves.

As more women enter the life sciences and medicine (in the UK, female undergraduates are in the majority in medical schools), this is changing. A study published in September 2016, for example, looked into the role of inflammation in premenstrual syndrome and uncovered new ways in which women could be treated for it in the future. Two of the study’s three authors were female.

Medical research is improved when women are more involved, not only as researchers and doctors, but also as vocal patients. Science and medicine have often failed women in the past, largely because men dominated research and set the parameters for what was investigated. Periods are a perfect case in point. It’s no surprise that menstruation was ignored for so long when men didn’t experience it. Until a few years ago, it was routine for women not to be included in clinical studies for new drugs. Thanks to years of dedicated activism, this is no longer the case.

I’m still holding out for the miracle pill that will someday eliminate my period pain. Until then, I feel happier in knowing that this doesn’t have to be my silent burden any more – not when so many women across the world are bleeding without shame.

Angela Saini's new book, "Inferior: How Science got Women Wrong – and the New Research that's Rewriting the Story" is published by Fourth Estate