Find a small animal shampoo with natural oils, especially if you have to bathe them more than once a month. It’s important to clean your rat more than once a month if your rat has been ill or is elderly. However, be careful not to bathe your rat too often. If you bathe your rat too often, the supply of natural oils on your rat’s skin and fur may become depleted, causing your rat’s skin to get too dry. Be sure that you use baby shampoo or animal shampoo. [5] X Research source Regular shampoo used for humans can cause serious skin problems.