But times are a changin'.
This year has been epic for menstruation, with news and social media catapulting the once hush-hush topic into the open.
There's the woman who ran the London marathon without using feminine hygiene products, and the #PeriodsAreNotAnInsult hashtag that erupted after presidential candidate Donald Trump referred to GOP debate moderator Megyn Kelly as having had "blood coming out of her wherever."
Researchers say all the hullabaloo may help give women better and eventually more eco-friendly options in menstrual care.
"For people like me who have been studying menstruation for decades, we've never enjoyed this kind of attention before," says Chris Bobel, associate professor of women's and gender studies at the University of Massachusetts, Boston and president of the Society for Menstrual Cycle Research. "I wrote a book on menstrual activism five years ago that got no attention. But now it is."
Is it? Even though Cosmopolitan magazine says it's "the year the period went public," we were skeptical. But social media's been awash with the p-word, and when we checked the number of times the word "menstruation" was mentioned in five national news outlets, it more than tripled from 2010 to 2015, from 47 to 167.
One big moment came in April, when Kiran Gandhi, a Los Angeles-based musician and feminist, ran the London Marathon while on her period, without using any hygiene products. She wanted to let her blood flow freely to encourage women not to feel embarrassed about their periods.
"The fact that we've been able to talk about periods openly is the biggest step in the revolution," says Gandhi, who finished the race with a blot of blood on the crotch of her neon orange leggings. "So many people are weighing in about the problems they currently face with their periods. It makes people empowered to speak about their own bodies."
Then came the hashtag #PeriodsAreNotAnInsult.
"That was a huge watershed moment for me," says Bobel of the online reaction to Trump's comment after the GOP candidates' debate in August. "Women were refusing to take the bait that menstruation is a put-down or a silencer."
Indeed, when we looked on Twitter the other day, we found that women are still toying with Trump with statements like: "It's normal and natural. Let's change the conversation. Let's break the taboo."
So maybe in an odd way this controversial candidate will help improve the options we women have for absorbing our periods.
"In America we have a new iPhone every year, but in the past two centuries there have only been three innovations in menstrual care. It's baffling," says Gandhi.
She's talking about the disposable sanitary pad, which was first marketed in 1888; the tampon, which became commercially available in the 1930s; and the menstrual cup, which has been around for decades but didn't become popular until softer versions were developed in the 1980s. (The adhesive pad was introduced in the 1970s.)
About two-thirds of American women use pads, according to data from the Centers for Disease Control and Prevention, while one-third use tampons. Those proportions include women who use both. And while most women use conventional products, entrepreneurs are busy creating new options.
"The interest in alternatives is greater than ever before," says Cynthia Pearson, executive director of the National Women's Health Network. "The number of questions we get about it — it seems like there's a new surge in interest. More folks are questioning whether to use tampons or push for getting more info about what's in them."
Rep. Carolyn Maloney, a New York Democrat, has been trying to find that out for almost 20 years. In April, she reintroduced legislation — for the ninth time since 1997 — that would require manufacturers to label the fabrics, colorants, dyes and preservatives used in pads and tampons. Some women have expressed concern that trace amounts of the toxic chemical dioxin could be in tampons as a byproduct of rayon processing.
The Food and Drug Administration, which regulates the manufacture of menstrual products, says changes in manufacturing processes intended to reduce dioxin pollution in the environment have made the materials in the products essentially free of dioxin. "FDA's risk assessment indicates that this exposure is many times less than normally present in the body from other environmental sources, so small that any risk of adverse health effects is considered negligible," according to the agency's website.
And then there's the question of the cost and environmental impact of using disposables. Women bought $3 billion of disposable sanitary products in 2014, according to the market analysis firm Euromonitor, a cost per woman of about $33 a year. Reusable products could cut into both purchase and disposal costs, and there are growing numbers on the market.
In June, CVS started carrying the $40 DivaCup, a reusable menstrual cup made of health care-grade silicone. Sales in dollars and units have been growing in double-digit rates, says Daniela Masaro, brand marketing manager of Diva International, the product's manufacturer.
There are also Thinx, underpants that use patented technology that the company says absorbs up to two tampons' worth of liquid while keeping women's clothes dry.
Since the startup launched in May with funding from a Kickstarter campaign, Thinx has sold 200,000 pairs of thongs, boy shorts and panties, which sell for about $30 a pop on its website. Most of its customers are women ages 24 to 34.
Women are also making their own reusable, washable pads, says Sharra Vostral, an associate professor of history at Purdue University and author of Under Wraps: A History of Menstrual Hygiene Technology.
Indeed, a quick search on Etsy, the online marketplace for homemade goods, yields nearly 4,500 results for an array of menstrual pads made out of fabrics like flannel and hemp.
But supermarket pads and tampons aren't going away anytime soon.
The new reusable products haven't solved all the hangups that come with being on your period. Women who have a heavier flow may need to use a backup tampon or pantyliner while wearing Thinx underwear, the company says.
And women who use a menstrual cup may have to clean the device in the sink of a public bathroom, making it an awkward choice for work or school. The cup might also dislodge an IUD, the manufacturer says.
Traditional menstrual care brands are trying to innovate, too.
Procter and Gamble, the dominant force in the market with its Always and Tampax brands, pays close attention to the features its consumers want, says Laura Dressman, a company spokeswoman. In 2008, the company introduced the Always Infinity pad, a super thin foam pad that absorbs 10 times its weight.
And in October, P&G and Kimberly-Clark — which together control the biggest segment of the $3 billion feminine care industry in the U.S. — decided to list ingredients for their pads and tampons.
That was a big win for activists including Gandhi, who had traveled to P&G's headquarters in Cincinnati to take part in protests demanding disclosure.
But for her, the fight won't be over until society conquers the stigma of menstruation.
"What I've learned over the past few months is that taboo removes the vocabulary for people to talk about their own bodies," she says. "If you can't talk about the problem, how can you talk about the solution?"
— via NPR