If a corn has broken open, you should not continue to apply corn plaster to it, as the plaster is somewhat corrosive. Since the skin of the corn has already been damaged, you should not use this medicated plaster until the skin has healed. Corns typically develop on the skin due to prolonged friction and pressure on the foot skin. Wearing ill-fitting shoes for a long period, or having deformed feet or toes, can also lead to the development of corns. If you have a corn, you can apply corn plaster locally, or visit a formal hospital to receive treatments such as cryotherapy with liquid nitrogen or using a carbon dioxide laser. If the corn has broken open, pay attention to the cleanliness and hygiene of the foot to prevent further infection. You can apply iodine locally for disinfection.