Because the bacteria that cause leprosy multiply very slowly, symptoms usually do not begin until at least 1 year after people have been infected. On average, symptoms appear 5 to 7 years after infection but may take 20 to 30 years. Once symptoms begin, they progress slowly.

Leprosy affects mainly the skin and peripheral nerves. Characteristic rashes and bumps develop. They are not itchy. Infection of the nerves makes the skin numb or the muscles weak in areas controlled by the infected nerves.

Specific symptoms vary depending on the type of leprosy.

Tuberculoid leprosy: A rash appears, consisting of one or a few flat, lighter areas with sharp, raised borders. Areas affected by this rash are numb because the bacteria damage the underlying nerves.

Lepromatous leprosy: Many small or larger raised bumps of variable size and shape appear on the skin. There are more areas of numbness than in tuberculoid leprosy, and certain muscle groups may be weak. Much of the skin and many areas of the body, including the kidneys, nose, and testes, may be affected. In affected men, the breasts may enlarge. People may lose their eyelashes and eyebrows.

Borderline leprosy: Features of both tuberculoid and lepromatous leprosy are present. Without treatment, borderline leprosy may become less severe and more like the tuberculoid form, or it may worsen and become more like the lepromatous form.

The most severe symptoms result from infection of the peripheral nerves, which causes deterioration of the sense of touch and a corresponding inability to feel pain and temperature. People with peripheral nerve damage may unknowingly burn, cut, or otherwise harm themselves. Repeated damage may eventually lead to loss of fingers and toes. Also, damage to peripheral nerves may cause muscle weakness that can result in deformities. For example, the fingers may be weakened, causing them to curve inward (like a claw). Muscles may become too weak to flex the foot—a condition called footdrop. Infected nerves may enlarge so that during a physical examination, doctors can feel them.

Images of Leprosy Tuberculoid leprosy causes a rash consisting of lighter areas with sharp, raised borders. Areas affected by this rash are numb because the bacteria damage the nerves underneath. CNRI/SCIENCE PHOTO LIBRARY In this person, leprosy has caused part of the fingers of both hands to be lost. Image courtesy of Arthur E. Kaye via the Public Health Image Library of the Centers for Disease Control and Prevention. In this person, leprosy has caused the cartilage in the nose to disintegrate. Image courtesy of Dr. Andre J. Lebrun via the Public Health Image Library of the Centers for Disease Control and Prevention.

Skin infection can lead to areas of swelling and lumps, which can be particularly disfiguring on the face.

Other areas of the body may be affected:

Feet: Sores may also develop on the soles of the feet, making walking painful.

Nose: Damage to the nasal passages can result in a chronically stuffy nose and nosebleeds and, if untreated, complete erosion of the nose.

Eyes: Damage to the eyes may lead to glaucoma or blindness.

Sexual function: Men with lepromatous leprosy may have erectile dysfunction (impotence) and become infertile. The infection can reduce the amount of testosterone and sperm produced by the testes.

Kidneys: The kidneys may malfunction. In severe cases, kidney failure may occur.