Calluses are areas of thickened and roughened skin that appear due to constant pressure or friction. They usually form on the feet: under the toes, on the heels, on the pads. Calluses themselves are not dangerous, but they can cause pain, discomfort, and become the cause of more serious problems. What are calluses Calluses are dry corns without a clear core. The skin at the point of pressure thickens, becomes rough and hard. Unlike wet corns, calluses do not contain fluid. ... Read more