Your mother has your best interests in mind. She may have received the instructions from your doctor on how to care for your broken arm. Communicating openly with her is a key to understanding the motives for recommending a sponge bath rather than a shower. Next time you have a follow up appointment with your doctor ask him or her about the best ways on maintaining hygiene with an arm cast. Your doctor may give you a written patient education materials on how to waterproof your cast and take a shower without compromising cast’s integrity. If you show your mother that you understand how to properly care for your cast she will be more inclined in letting you to take a shower rather than a sponge bath.