Is it OK to file a callus all the way down, or should I leave some?

In my podiatric office, I file most of the callus off, but I find in the summer, some thickness on the bottom of the foot is needed to wear open-toed shoes. Calluses develop from the friction of walking. They are for protection. However, when there is too much callus, it can act as an irritant and cause an ulcer (sore) to form underneath, especially in people with diabetes or other circulation problems. So, in the summer, take less off the callus and allow some to remain for the body’s natural protection. In the winter, when socks and shoes are worn, you can take off more. -- Dr. Johanna Youner