Girls in the UK are missing school because they cannot afford sanitary protection, a charity has said.
Freedom4Girls was contacted by a school in Leeds after it became concerned about teenage girls' attendance.
The group provides sanitary products to women in Kenya - but is now doing the same in West Yorkshire.
One teenager told the BBC she taped toilet roll to her underwear and missed school "every month" because of her period.
Two teenage girls spoke to BBC Radio Leeds about how they tried to cope without tampons, sanitary towels or pain relief.
One of the girls said: "I wrapped a sock around my underwear just to stop the bleeding, because I didn't want to get shouted at. And I wrapped a whole tissue roll around my underwear, just to keep my underwear dry until I got home. I once Sellotaped tissue to my underwear. I didn't know what else to do.
"I kept this secret up until I was 14 years old and then I started asking for help.
"I didn't get any money because my mum was a single parent and she had five mouths to feed, so there wasn't much leftover money in the pot to be giving to us."
She had started her period at the age of 11. She said she would take a few days off school every month.
Another teenager said: "When I went on my period I started taking time off school, because I didn't know what was actually going on with my body. That made my attendance really low and I was getting in trouble.
"One day the teachers came to my house and asked why I'm not at school and they actually took me to school.
"I thought it was only happening to me... so I was scared and I wanted to stay at home."
She said she had an "amazing" teacher who helped her through everything, from family problems to periods.
'Give dignity back'
Tina Leslie, a public health worker in Leeds and part of Freedom4Girls, said she was contacted by the teacher from a south Leeds school, about three weeks ago.
She was able to arrange for sample packs to be sent to the school but admitted it was "not a sustainable solution".
"I wasn't shocked at all," she told BBC Radio 4's Woman's Hour. "We had an idea that there was something happening in schools. It's linked to poverty - 25,000 visits to food banks just in Leeds last year.
"We need to give these girls dignity back."
Ms Leslie said it was unclear how many girls were in this situation in the UK, and more research was needed.
She said: "It's happening in other schools. Teachers have told me they are buying towels to have just in case.
"If you've got no food, you've got no money for sanitary protection. If you have a mum with two teenage girls, that's a lot of money each month when you're on zero-hours contracts, benefits or low income.
"It's the working poor that we are looking at."
Conservative MP Jason McCartney has since said he will raise the issue in Parliament.
He wants to enlist other MPs to help start a campaign for free sanitary products for young girls in need.
Elsewhere, Labour MSP Monica Lennon is calling for sanitary products to be given out free in Scotland.
She told Woman's Hour: "We are trying to establish a principle here, that this is a health issue.
"If you go to a food bank or homeless shelters, they know people who are having to go without."
Sanitary protection donation in the UK:
- Manchester-based The Monthly Gift is a campaign increasing donations of sanitary products to charities helping the homeless and those in poverty
- Bloody Good Period collects period supplies and toiletries for asylum seekers, refugees and those who can't afford them
- You can donate money or tampons to The Homeless Period
- Food banks like the Trussell Trust also accept towels and tampons