Your vagina is a very permeable membrane and everything you expose it to can get into your bloodstream. This includes chemicals, bleach, dioxins, fragrances, plastics, and pesticides since cotton is one the most sprayed crops. Most conventional tampon producers don't have to disclose what is n their tampons because it is considered a "medical device". Ingredients like dioxins have been linked with cancer and fragrances are endocrine disrupters that can mess with your hormones.
We did a little experiment where we soaked tampons in water overnight to see what would happen. It was kind of shocking. You can see the results here.
We prefer organic cotton tampons from Natracare that are pesticide-free. Plus we love that they contain no plastic and are biodegradable. Good for you and good for the planet.