Causes, Symptoms And Treatment Of Corns And Calluses! - Renaissance Skin Hair Laser Clinic by Dr Sarita Tippannwar. Corns and calluses are defined as thickened and hardened areas of the skin, which are formed due to excess pressure, friction or rubbing in a particular area. They generally form at the bottom of the feet and can cause discomfort and pain while walking. Corns usually form on the sides and tops of toes.