Rabies is a rare but serious disease caused by a virus. The virus that causes rabies is carried in saliva.

Radiation Injuries

Radiation injuries are damage to the body caused by ionizing radiation. Ionizing radiation (IR) is given off by the sun, X-ray machines, and radioactive elements.

Reye's Syndrome

Reye's syndrome is a disorder that primarily affects the liver and brain. It attacks the nervous system very quickly and can cause death.

Rheumatic Fever

Rheumatic fever (RF; pronounced roo-MAT-ic FEE-ver) is a disease caused by a group of bacteria known as Group A streptococcus (pronounced STREP-tuh-cac-us). The exact conditions that lead to rheumatic fever are not well understood.


Ringworm is a common infection with a misleading name. The disease is actually caused by a fungus, not a worm.


Rubella (pronounced roo-BELL-uh) is a highly contagious (catching) viral disease also known as German measles. It is spread through contact with discharges from the nose and throat of an infected person.

Scarlet Fever

Scarlet fever is an infection caused by a bacterium called Streptococcus (pronounced strep-tuh-KOK-us). The disease is characterized by a sore throat (see sore throat entry), fever, and a sandpaper-like rash on reddened skin.


Schizophrenia (pronounced skit-suh-FREH-nee-uh) is a psychotic disorder or group of psychotic disorders that cause a patient to lose touch with reality. It is marked by severely impaired reasoning and emotional instability and can cause violent behavior.


Scoliosis (pronounced SKO-lee-OH-siss) is a side-to-side curvature of the spine (backbone).

Seasonal Affective Disorder

Seasonal affective disorder (SAD) is a form of depression (see depression entry) most often associated with the lack of daylight. The condition usually occurs in the extreme southern and northern latitudes from late fall to early spring.

Sexually Transmitted Diseases

A sexually transmitted disease (STD) is a disease transmitted through sexual contact between two people. They may be transmitted through the exchange of semen, blood, and other body fluids or by direct body contact.

Shaken Baby Syndrome

Shaken baby syndrome (SBS) refers to a combination of injuries that occurs when a baby or young child is violently shaken.

Sickle Cell Anemia

Sickle cell anemia is an inherited blood disorder in which the body produces c-shaped red blood cells. Because of their shape, these cells may stick to each other or to the sides of blood vessels, and cause serious health disorders.

Skin Cancer

Skin cancer is a malignant growth on the outer layer of the skin. A malignant growth is one that has the potential to cause death.

Skin Disorders

Skin disorders include a variety of medical problems associated with the skin. Three common forms of skin disorder are dermatitis, psoriasis (pronounced suh-RY-uh-siss), and vitiligo (pronounced vit-ihl-EYE-go).

Sleep Disorders

Sleep disorders are a group of conditions characterized by disturbance in the amount, quality, or timing of a person's sleep. They also include emotional and other problems that may be related to sleep.


Smallpox is an infection caused by the virus called variola (pronounced vuh-RY-uh-luh). Throughout history, smallpox has been a greatly feared disease.

Smoke Inhalation

Smoke inhalation is breathing in smoke. Smoke contains many substances that can cause damage to the human body.

Sore Throat

Sore throat is a painful inflammation of the pharynx. The pharynx (pronounced FAAR-ingks) is the part of the throat that lies between the mouth and the larynx (pronounced LAAR-ingks), or voice box.

Spina Bifida

Spina bifida (pronounced SPI-nuh BIFF-ih-duh) means an open or severed spine and it is one of the most serious of all birth defects. The condition may affect a small region of the spine or a much larger area.

Spinal Cord Injury

Spinal cord injury is damage to the spinal cord that causes loss of sensation (feeling) and motor (muscular) control.

Strep Throat

Strep throat is an infection of the pharynx (pronounced FAAR-ingks). The pharynx is the part of the throat that connects the mouth and the larynx (pronounced LAAR-ingks), or voice box.


A stroke is the sudden death of cells in a limited part of the brain caused by a reduced flow of blood to the brain.

Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) is the unexplained death of an apparently healthy infant, usually during sleep. The condition is also known as crib death.

Tay-Sachs Disease

Tay-Sachs disease (pronounced tay-SACKS) is a genetic disorder that can lead to paralysis, blindness, convulsions, mental retardation (see mental retardation entry) and death. A genetic disorder is a medical problem passed down from one generation to the next.

Temporomandibular Joint Disorders

Temporomandibular joint disorder (TMJ) is a group of symptoms that involve pain in the head, face, and jaw. Symptoms of TMJ include headaches, soreness in the chewing muscles, and clicking or stiffness of the joints.


Tendinitis (pronounced tehn-duh-NI-tiss) is the inflammation of a tendon. Tendons are tough, rope-like tissue that connect muscle to bone.


Tetanus (pronounced TET-n-uhss) is an infection of the central nervous system (the brain and spinal cord). The disease is rare, but often fatal.


Tonsillitis (pronounced tahn-suh-LIE-tiss) is an infection and swelling of the tonsils. The tonsils are lymph nodes, or oval-shaped masses of lymph gland tissue, located on both sides of the throat that are part of the body immune system.

Tooth Decay

Tooth decay is the destruction of the enamel (outer surface) of a tooth. Tooth decay is also known as dental cavities or dental caries.

Tourette Syndrome

Tourette syndrome (TS; pronounced ter-ET sin-drohm) is an inherited disorder of the nervous system. It is named after the French physician George Gilles de la Tourette who first described the condition more than a century ago.

Toxic Shock Syndrome

Toxic shock syndrome (TSS) is an uncommon, but potentially serious, illness. It almost always occurs in women using super-absorbent tampons during menstruation, but researchers are still not entirely clear what the connection is between this kind of tampon and TSS.


Tuberculosis (pronounced too-BUR-kyoo-LOH-siss), or TB, is a contagious disease of the lungs that can spread to other parts of the body and may be fatal. TB is caused by a microorganism known as the tubercle bacillus, or Mycobacterium tuberculosis.

Ulcerative Colitis

Ulcerative colitis (pronounced UHL-suh-RATE-ihv kuh-LY-tiss) is an inflammation of the large intestine that causes swelling, ulcerations (open sores), and loss of function in the large intestine.


An ulcer is any break in the skin or in a mucous membrane. Mucous membrane is a thin tissue that lines the interior surface of body openings.

Vision Disorders

Vision disorders are conditions caused by the eye's inability to properly focus light rays. Three major types of vision disorder are hyperopia (pronounced HY-puh-ROH-pee-uh), or farsightedness; myopia (pronounced my-OH-pee-a) or nearsightedness; and astigmatism, which causes the eye to form a blurred image of an object.


Warts are small, benign (harmless) growths caused by a viral infection. They occur on the skin or the mucous membrane.


Whiplash is an injury that occurs when the neck and head experience a sudden, sharp motion. The injury often affects the bones, muscles, nerves, and tendons of the neck.

Whooping Cough

Whooping cough is a highly contagious disease caused by bacteria. The disease is also known as pertussis (pronounced pur-TUSS-iss).

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