The most urgent tampon health concern is that chlorine-bleached and rayon-containing products carry trace amounts of dioxin, an extremely toxic chemical that is associated with cancer of the stomach, sinus lining, liver and lymph system. Many people are familiar with the danger of dioxins from publicity about Agent Orange and the Love Canal catastrophe.

Tampons are linked to carcinogenic dioxin formed during the bleaching process that manufacturers use to purify and whiten both raw cotton and the wood pulp that goes into synthetic fibers such as rayon, a common fiber in tampons. "You find trace amounts of dioxin in some tampons, which have maximal contact with the vagina's mucous membrane, which absorbs substances directly into the bloodstream," explains Philip Tierno, MD, director of clinical microbiology and immunology at New York University Medical Center.

How to avoid dioxin

To ensure that your tampon is free of dioxin, switch to a brand that's nonchlorine-bleached, rayon-free, and made of 100 percent-organic cotton. Though cotton is a natural fiber, the majority of cotton crops are heavily treated with insecticides, pesticides and herbicides. Organically grown cotton is not.

Check your tampon box for a list of ingredients. Whereas natural brands state that they're nonchlorine bleached, some conventional brands mention little on the subject, because along with the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA), they believe chlorine-dioxide bleaching is safe.

Tierno disagrees: While trace quantities of dioxin aren't in and of themselves a problem, tampons aren't your only exposure. "The problem is that measurable amounts of dioxins are everywhere, including food and water. Some portion of the dioxin that enters your bloodstream lodges in the body's fat cells and stays there a long time," he says. "This residual effect becomes progressively larger as you're exposed to even more dioxins."

The only way to avoid vaginally absorbed dioxin, Tierno says, is to eliminate chlorine-bleached and rayon-containing tampons and switch to peroxide-bleached products instead. Tierno also says if the label on your tampon box doesn't say "nonchlorine-bleached," it's possible that it contains chlorine. Most manufacturers proudly promote the fact that their product doesn't contain chlorine.

Dioxin's risks

The cumulative risks of dioxin are unknown. While a single tampon may contain only 0.1 parts per trillion of dioxin, the fact that most women use between 10,000 and 15,000 tampons in a lifetime increases the exposure.

"A trace quantity of dioxin is not acceptable in a tampon, because a woman does not expose herself to a single tampon," Tierno says. "It's trace quantity upon trace quantity upon trace quantity, multiplied by the number of tampons per month, multiplied by the number of months in a year, multiplied by 40 years of menstruation. Then add in all the dioxins you get from your diet, plus all the ones occurring in the environment."