Years ago, as a law student, I became so irked about being taxed on tampons and not chapstick that I researched the New York law. That research became the basis for a class action lawsuit filed last year challenging the state’s tampon tax, and prompted my joining a growing group of “menstrual equity” advocates. We celebrated the end of New York’s sales tax on feminine hygiene products this past fall and have set our sights on the 37 states that still burden women in sales tax overcharges by an estimated $120 million annually.

Through my work on this issue, I’ve come to believe that tampons aren’t just harming women’s finances. Commercially marketed tampons, made of toxic materials, may be seriously endangering women’s health. There are safer products now entering the market, but they cost more—and over and above the already unrealistic price of menstrual supplies of any quality for tens of millions of American women.

How serious is the problem with commercial tampon brands? Exposure to environmental toxins via tampons inserted in the vagina has never been thoroughly studied, but what we do know is alarming. The vaginal mucous membrane is not only more vulnerable to toxic chemical exposure than ordinary skin, but it’s also more vulnerable even than the mouth: Drugs are absorbed into the body over 10 times more efficiently through the vagina than when taken orally. Recently there’s been a barrage of successful lawsuits against Johnson & Johnson by women diagnosed with ovarian cancer linked to—shockingly—baby powder. Regular use on the vagina led in some cases to death.

Cancers and auto-immune disorders linked to environmental toxins have increased dramatically in the last several decades when, perhaps not coincidentally, tampon use among menstruating American women has risen to 70 percent. The average American woman will, over the course of her life, wear a tampon for the equivalent of six years, full-time.