There are a variety of dermatological conditions that could cause dry, flaky skin, such as athlete's foot. However, the most common cause of thickened skin on your feet is a callus. The reason calluses develop is to help protect your feet from pressure points or friction. However, at some point the callus can get so thick than it can hurt the underlying skin, and can even start causing sores, so it's a good idea to shave those calluses down before they get too thick.