Leprosy is a rare disease in which bacteria (Mycobacterium leprae) attack the skin, nerves, and mucous membranes, such as the eyes. People with leprosy develop sores on their skin and lose some of their nerve sensations.

Leprosy is also known as Hansen's disease.

The progression of leprosy depends on its type:

• Tuberculoid leprosy is a mild form of the disease. It causes mainly skin problems and a thickening of the nerves close to the skin.
• Lepromatous leprosy is a more severe and widespread form of leprosy. It can affect many parts of the body, resulting in the destruction of bone and cartilage, development of lumps under the skin, and blindness.

Leprosy is treated with medicine, which may control how quickly it progresses but rarely resolves symptoms completely.