Pressure and friction from repetitive actions cause corns and calluses to develop and grow. Some sources of this pressure and friction include:
Wearing ill-fitting shoes. Tight shoes and high heels can compress areas of your feet. When footwear is too loose, your foot may repeatedly slide and rub against the shoe. Your foot may also rub against a seam or stitch inside the shoe.
Skipping socks. Wearing shoes and sandals without socks can cause friction on your feet. Socks that don't fit properly also can be a problem.
Playing instruments or using hand tools. Calluses on your hands may result from the repeated pressure of playing instruments, using hand tools or even writing.