Tropical ulcer on a patient's left leg. Tropical ulcers develop from cuts that become infected with a variety of micro-organisms. They are particularly prevalent during rainy seasons in the tropics because wounds are unable to dry out and become infected easily. A large, painful ulcer with raised edges rapidly develops at the site of infection. If it is less than 5 centimetres in diameter, the ulcer can be treated with pencillin antibiotics and dressings. However, when an ulcer is larger than this, and underlying muscle and bone has been exposed, skin grafting is necessary.