Corns and calluses are caused by pressure or friction on your skin. They often appear on feet where the bony parts of your feet rub against your shoes. 
Wearing shoes that fit better or using non-medicated pads may help. While bathing, gently rub the corn or callus with a washcloth or pumice stone to help reduce the size. To avoid infection, do not try to shave off the corn or callus. See your doctor, especially if you have diabetes or circulation problems.