Infectious disease caused by the Mycobacterium leprae bacillus. The disease, once known as Hansen’s disease, occurs throughout almost the whole of the tropics and subtropics, and there are 15 million sufferers. Infection takes place via the skin and mucous membranes, by contact with infected persons who spread the bacteria by coughing, sneezing and nasal discharge. The chance of infection is increased by poor hygienic conditions and it is usually young people that are affected. Manifestations of the disease vary with the degree of resistance of the patient. The bacillus establishes itself in the skin and nerves in particular. Many cases of leprosy begin three to five years after infection with unusual sensations in certain parts of the body, which become lighter in colour than the rest of the skin. Often the disease is confined to several small, clearly delineated areas of skin, and several small nerves are affected. Hair falls out and less sweat is produced in the affected areas. This form of leprosy heals spontaneously in a short time. In patients with reduced resistance the areas of skin are larger and more nerves are affected. The skin abnormalities can then consist of lumps, particularly on hands, feet and face. Finally the bacteria can spread throughout the body. Mutilation is mainly the result of the affected nerves causing loss of hair and paralysis. The patient does not feel pain, which results in wounds and burns on hands and feet, which are then open to infection by various bacteria, which finally leads to malformation. Tingling and a dead feeling in hands and feet, twisted fingers or toes, ulcers on the palms of the hand and the soles of the feet are all manifestations of leprosy. Leprosy can be healed by timely and careful medication, which must be continued for four to five years. The condition ceases to be infectious shortly after treatment begins, but damaged nerves do not recover. Local abnormal development of the mucous membrane of the mouth (hyperkeratosis), with a white-colouring. The cause is often long-term irri-tion of the mucous membrane at a particular point – by badly-fitting dentures or smoking, for example. As a rule leucoplakia causes few or no symptoms; sometimes a rough, thicken- ed spot can be felt in the mouth, often found only by chance. Because there is a danger that a malignant tumour might be formed it is advisable to have a piece of the tissue removed for microscopic examination (biopsy), so that a correct diagnosis can be made. Treatment is by removal of the irritant. If the spot does not disappear it is recommended to remove it by surgery; otherwise regular checks will continue to be necessary because the tumour could become malignant.