I apply butter LONDON's Rock Away callus remover and wrap my feet in Saran wrap, as the technician in Seattle did. Potassium hydroxide is listed as the second ingredient after water, so this is a caustic solution.
butter LONDON Rock Off Callus Remover
At bedtime, I then apply butter LONDON's Stiletto Stick to my feet and put on socks. Other options are thick creams enriched with urea such as Eucerin Plus.
butter LONDON Stiletto Stick
Repeated treatment leaves feet smooth and uncallused.
You may find butter LONDON at Beauty.com and Eucerin Plus at beauty.com's sister site drugstore.com, major drugstore and supermarket chains, and "big box" stores such as Target and Wal-Mart.