Tampons are designed to expand when they touch liquid, meaning when a tampon is flushed down a toilet, it can expand to multiple times the size of a dry tampon. This can create blockages in the sewerage system, which can not only be expensive to repair but also have serious health implications because of the backflow. Toilet paper is specifically designed to break down almost immediately after making contact with liquid, however, tampons are designed to hold together despite hours of contact with liquid.