"Nothing should stand in the way of a girl and her education": Sophia Bush is fighting to end period poverty in the U.S.

For the average woman, who spends 2,535 days of her life menstruating, periods may just be a slightly painful inconvenience. But for millions of other girls and women in the U.S., the cost of period products has become a barrier to everyday existence.

American women are 38% more likely to live in poverty than men — and most states do not exempt pads, tampons and menstrual cups from sales tax, leaving women across the country without access to essential products. Period poverty has quietly become a nationwide epidemic, and now celebrities are starting to take action. 

"I truly believe nothing should stand in the way of a girl and her education," Sophia Bush wrote on Instagram. "Nothing! Certainly not her period." The actress and activist recently committed to helping end period poverty, specifically for girls trying not to miss school simply because they are bleeding. 

"Period poverty affects girls EVERYWHERE," she wrote. "And I believe that we have to bring awareness to this disparity so we can actively start solving this education crisis."

According to a survey The Always Confidence and Puberty Wave VI, nearly one in five girls in the by  U.S. have missed school due to a lack of period products. "I was aghast" to learn that, Bush said. 

Bush is partnering with Always, which makes period products, to raise awareness about just how widespread the issue is. She plans to help them surpass last year's donation of 20 million products to girls across the country. 

While many people believe period poverty isn't an issue in the U.S., 143,0000 girls in New York City alone have missed school due to a lack of access to menstruation products, according to Always. The number is 88,000 girls in Los Angeles, 65,000 girls in Chicago, 57,000 girls in Atlanta, and 38,000 girls in Houston. 

"If you have to pick and choose, do I buy food for my child or do I get my sanitary needs, that's kind of hard and no one should have to experience that," Brooklyn native Nicole Johnson, who went into a homeless shelter in 2005 with her four children, told CBS News. "It's demeaning. It makes you feel very sad. ... It's a heartbreaking situation."

"If you can't even put a loaf of bread on the table, how do you expect a person to buy a box of tampons that may be $5 and change?" Johnson said. "Most people don't stop and think about it. I guess they feel they're able to get their own pads and tampons. It's the littlest things that people don't focus on. Yes, you need food, you need water. There's plenty of soup kitchens. But the personal items, the sanitary napkins, the soap, the toothpaste, deodorant… it's not that easy for people."

Actress and women's rights advocate Busy Philipps has also taken up the cause, bringing the issue to national television. 

"Something that happens to half the population once a month shouldn't be a taboo subject," Philipps told CBS News. "I mean, to be totally honest, and I'm sure I'm not the first person to say this, but like if men had their periods, it would be like f***ing celebrated. You know, it would be like a holiday." 

In March, Congresswoman Grace Meng of New York announced the Menstrual Equity for All Act before Congress, the first comprehensive bill addressing the challenges that women face in obtaining period products. The bill would make menstrual products free for women in prison, allow states to use federal funds to supply pads to girls in school and require that these products be covered by Medicaid.

"The fact that there are people who aren't able to afford these products, and as a result, may miss school, may miss work, face certain stigma — I think it's a human rights issue that, especially in the United States of America, women should not have to be dealing with," Meng said.