I wonder for sanitary reasons. Is my sister just pushing germs around by using the same old sponge to wash dishes? I have been using a dish rag, that I hang to dry between loads of dishes. It never smells like mold/ mildew. On the other hand my sisters sponge smells like mold or mildew. Even after a few days. She says it is ok that she changes it every month. Neither one of us has a dishwasher, as I understand that is the most sanitary way. Does any body have information on the cleanliness of a sponge?