London — Seven years ago, Rachel Krengel was a young mother with two small children. Facing a delay on welfare payments, she and her family were struggling to stay afloat.

"We fell into this awful spiral of poverty and debt," says Krengel. "One of the things that fell by the wayside was my ability to buy enough menstrual products to get me through the month."

Sitting in her living room in Croydon, south London, the 30-year-old feminist and political activist recalls how she kept the problem a secret out of shame and an ingrained belief that periods are taboo. She now campaigns to make sure women don't experience the same challenges.

"I never talked to anyone at the time," she says. "I never told my partner that it was an issue."

Period poverty -- where girls or women are unable to afford sufficient menstrual products -- is often seen as a problem confined to developing countries. In Tanzania, for example, many girls and women say basic pads are simply unaffordable.

But recent surveys in the UK have exposed startling rates of period poverty in one of the world's richest countries and sparked a national conversation.

With a contraceptive implant that made her bleed at least 25 days out of every 28, the problem was particularly acute for Krengel.

Krengel rationed her menstrual products, wearing a single sanitary pad for up to 20 hours (instead of the recommended three or four), inserting a contraceptive diaphragm to catch the blood or simply free bleeding (using nothing at all).

Throwing away her old jeans later, she noticed that "all of them had this red stain running down the seam, because I would just be free bleeding at least two or three days every week."

Like countless girls and women around the world who miss days of school or work every month because they can't access the products they need, Krengel found herself spending more time at home, worried about going out.

Menstrual products and other toiletries in Krengel's bathroom. Photo: Sarah Tilotta for CNN

'The first thing under the bus'

At the time, Krengel, her partner and their two daughters -- one of whom was just a few months old -- were living in Norwich, a small city 100 miles northeast of London.

Switching between two different types of welfare, the family's housing benefit was paused and they were told to reapply. But there was a months-long backlog: "We were left without any money to pay rent for a very long time," Krengel recalls.

They turned to high-interest payday loans and friends and family to keep food on the table and a roof over their heads.

When they had no money for food, Krengel's brother-in-law did an online grocery shop. When her two-year-old daughter had no winter coat, Krengel's sister went out and bought one.

But when she had no menstrual products, no one knew and so no one helped.

"Any time someone was offering to help us financially, I would say, 'go buy something for the kids.'"

And it was often a choice between spending £1 ($1.30) on a packet of sanitary pads or putting food on the table, she says.

"You can make dinner for four people for £1," she says. "That seemed so much more important than something that was only for me."

Menstrual products are "the first thing that goes under the bus when you're poor."

'Tip of the iceberg'

The research was triggered by media reports last March that some schoolgirls in Leeds, a city in northern England, were missing up to a week of school every month because they could not afford menstrual products. Others were regularly using tissue paper or socks instead of pads or tampons.

"We know of a few hundred cases (of girls unable to afford menstrual products)," says Sharon White, head of the UK's School and Public Health Nurses Association. "But that's the tip of the iceberg."

And it's a problem that can impact women of any age. Many UK food banks now offer non-food items such as menstrual products and the demand for them is growing significantly, explains Alison Inglis-Jones, trustee and volunteer at the Trussell Trust, which runs more than 420 food banks across the country.

A protest in London last December called for an end to period poverty in the UK. Photo: Judith Vonberg for CNN

"I've seen people coming in using newspaper, tissues or socks," she says. "One woman was taking paper out of a public library and using that."

"If you can't afford food you can't afford sanitary protection," says Tina Leslie from Freedom4Girls, the charity that first flagged the issue among UK schoolgirls last year. "The problem is the same here as it is in Kenya."

And poverty is on the rise in many more developed countries, partly due to a decade of spending cuts.

Current trends show that the long-term policy of austerity in the UK, largely implemented by Conservative-led governments of the last eight years, has impacted women more significantly than men -- and women of menstruating age most of all.

According to the Equality and Human Rights Commission , many of them are mothers claiming child benefit and other forms of family welfare and therefore account for a big proportion of welfare payments -- that means they are hardest hit when payouts are cut.

But for many girls and women globally, financial poverty is compounded by the stigma around menstruation that leads women to "hand off tampons to each other like we're doing a drug deal," as Krengel puts it.

"Two massively stigmatized experiences -- menstruation and poverty -- intersect to create this bizarre and horrible form of poverty," she says.

She, like many others, believes both must be addressed simultaneously to have any long-lasting impact.

Tackling the taboo

Since Plan International released their UK study, long-running campaigns tackling the issue have been picking up more interest than ever before -- and new ones have sprung up too.

A protest in central London last December was a watershed moment for those campaigns, marking the first time the issue hit mainstream headlines in the UK.

The rally outside Downing Street, the official residence of Prime Minister Theresa May, attracted celebrities including British models Daisy Lowe and Adwoa Aboah and hundreds of demonstrators, some sporting tampon jewelry and vagina-related paraphernalia.

Hundreds turned out in London last December to protest against period poverty. Photo: Judith Vonberg for CNN

Many protesters told CNN they were shocked to learn that period poverty was a UK problem.

"It's disgraceful that our society's even having this problem and disgraceful that we should feel ashamed for talking about it," 18-year-old Suzie Murray said at the rally.

Chella Quint, who runs a campaign called Period Positive, encouraging shame-free conversations about menstruation, has only recently freed herself from that psychological trap.

"There were times when I couldn't financially afford menstrual products and that was worrying, and there were other times when I couldn't socially and culturally afford it, because I was afraid to say anything," she says.

Not having loads of toys as a child "didn't harm me forever I don't think," Quint explains. "But the embodied shame around feeling negative about periods -- that definitely has."

Rachel Krengel makes a similar point. "I think there's a part of every menstruator on this planet who is still a 12-year-old who's just spotted blood on their crotch and is so desperately ashamed of that."

Demonstrators at the December protest in London. Photo: Judith Vonberg for CNN

'It's so easy to fix'

With so much attention currently focused on women's issues and gender inequality, Krengel believes now is the time to push for change.

She wants to see free provision of menstrual products in all UK schools. By her calculation it would cost £11 ($14) per child per year.

"It's so easy to fix," she says. "It's a nothing amount of money."

petition started by Krengel and other members of the London-based feminist activist group Fourth Wave is calling on British Prime Minister Theresa May to introduce free menstrual products in all UK schools. It has gathered more than 135,000 signatures to date.

Scotland is set to do just that. In August, the Scottish government set aside £5.2 million ($6.8 million) to provide free sanitary products in schools, colleges and universities across the country.

Wales has also set aside £1 million ($1.3 million) for a similar project.

The UK's Labour Party -- the largest opposition party -- has pledged to spend £10 million ($13 million) to provide free sanitary products in secondary schools, homeless shelters and food banks. Smaller parties, including the Liberal Democrats, the Green Party and the Women's Equality Party, have made similar pledges.

In a debate in the House of Commons in June, Minister for Women Victoria Atkins said there was "no significant evidence" that period poverty was having an impact on school attendance.

"For (the government) to do something about it now would mean an acknowledgement that child poverty has soared over the last seven years," Krengel says. "It would be an admission of what austerity has done to our society."

Krengel with her daughters, Kitty, 9, (left) and Millie, 8. Photo: Sarah Tilotta for CNN

Along with free provision of pads or tampons, campaigners are calling for better education about periods in schools.

Krengel says that if these national conversations had been happening when she was struggling with period poverty in secret, it might have helped. She hopes people like her are feeling "a bit less alone now."

Krengel, who no longer experiences period poverty herself, says that if these national conversations had been happening when she was struggling in secret, it might have helped. She hopes people like her are feeling "a bit less alone now."

But while "not feeling alone is great, it has limited usefulness," she says. "What we need is some actual change. We need some action."

Clarification: This story has been updated to better reflect that activist Rachel Krengel no longer experiences period poverty herself and has organized a petition calling for free menstrual products in all UK schools.