The other day my friend loaned me an organic tampon and said that she'd heard that normal tampons have fiberglass in them to increase bleeding. (!!!) You know, so that the company sells more tampons?
Anyway, since that sounded totally absurd, I decided to sleuth a bit and according to a reputable looking source, (and the back of my box of tampons) there is no fiberglass in tampons but there can potentially be dioxins, which could potentially cause cancer, eventually. The dioxins can come from the bleaching process or from a rayon-cotton blend, or even from pesticides used on the cotton when it is growing. This is either dangerous because you are putting them on a very absorbent part of your body for quite awhile, repeatedly, or not something to worry about because there are dioxins & pesticides & harmful chemicals everywhere so the tiny amount in tampons are chump change. The latter view is the official FDA line, and I think I'll go with that, since I'd rather not worry about it.