I have endometriosis and also had uterine fibroid tumors (removed). I've done a lot of research on the potential causes of endometriosis and there is some pretty strong evidence which links endo with dioxin. Dioxin is a by-product of the paper-bleaching process and is present in most tampons and pads. Dioxin is also a carcinogen. The Endometriosis Association purchased a colony of monkeys that had been already researched on for dioxin-cancer links so that they could do their own research and see if there was any link to endometriosis. They found a direct correlation between the presence and degree of endometriosis and the amount of dioxin exposure in the monkeys!!!
If you want to be safe, use organic dioxin and chlorine free tampons and pads, or use glad rags (washable), sterilized sea sponges or a menstural cup like the Keeper.