What Harm Can Result From Regularly Eating Bath Sponges, And Why Might I Crave Them?

Hi I just want to know what damage can be done by eating sponges such as the ones used for a bath. I have had a craving for them and ate them most of my life. However, recently the craving has become overwhelming and if I dont gave any in the house I will have mood swings. Some weeks I may go through 1 and other weeks it might be up to 4 over the last few months. I am not pregnant so I know it is not this. I have not had any bowel issues so I am guessing they are digesting ok