Conjunctivitis is a common disorder in the United States, affecting one in every 50 people each year. Conjunctivitis has many different causes, including infections and allergies.


Normal bowel movement patterns vary from person to person. Some people move their bowels as often as after every meal.

Creutzfeldt-Jakob Disease (CJD)

Creutzfeldt-Jakob disease is a slowly progressing disease of the brain. While most people who contract the disease die within several months, some people decline slowly and may live several years after they are diagnosed.


The word croup is used to describe several conditions that cause a loud, barking cough and difficulty with breathing. Some croup-like conditions are caused by allergy, others may be caused by bacterial infections, but the majority of cases, about 75 percent, are caused by parainfluenza or other types of viruses.

Cushing's Syndrome

Cushing's syndrome is an endocrine, or hormone*, condition. It occurs when the body is exposed to high levels of the hormone cortisol for long periods of time.

Cyclosporiasis and Cryptosporidiosis

Thousands of people in Milwaukee, Wisconsin, started to get sick in early 1993. They had stomach pains, nausea, fever, and diarrhea, as if perhaps they had influenza.


Cysts may develop in many areas on the inside or outside of the body. They may be found in the mouth around a developing tooth, in the skin around a hair follicle or sweat gland, in other glands, in the spinal cord, in the liver, in bone tissue, in ovaries*, and in other parts of the body.

Cystic Fibrosis

Rachel's parents were worried. They believed they provided all the proper care Rachel needed, just as they had for their older daughter when she was a baby.


Cytomegalovirus (sy-to-MEG-a-lo-vy-rus) is a very common virus, with close to 85 percent of the U.S. population carrying antibodies to it, according to the U.S.

Deafness and Hearing Loss

Kathy Peck was a guitarist in the 1970s and 1980s in a rock band known as the Contractions. They played a mix of punk and new wave music in San Francisco and toured across the United States.

Dengue Fever

Dengue (DENG-gee, English; DAIN-gay, Spanish) affects millions of people each year in tropical and subtropical regions. It is especially common in southeastern Asia and is also found in Latin America and the Caribbean, including Puerto Rico.

Depressive Disorders

Even when the sun shines brightly, Jodie feels darkness everywhere she looks. She used to sleep so soundly that her father said he needed a cannon blast to wake her.


Melinda had just turned twelve and felt hungry all the time. Her stomach growled in class and her after-school snack no longer held her until dinner.


Diarrhea is very common, a condition with which almost everyone is familiar. Usually, it is little more than an unpleasant nuisance that briefly interferes with work or play.

Dietary Deficiencies

The human diet is divided into five nutritional groups: proteins, carbohydrates, fats, vitamins, and minerals. These five groups include about 50 nutritional items that are necessary for good health and growth.


Descriptions of diphtheria date from antiquity. The microorganism that causes it, a bacterium called Corynebacterium diphtheriae (ko-rin-ee-bak-TEE-ree-um dif-THEE-ree-eye), enters the body through the tonsils, nose, and throat, and multiplies there, producing a thick, gray membrane made of bacteria, dead cells, and a tough protein called fibrin that can eventually block breathing and swallowing.


The cause of diverticulosis is not known with certainty, but many physicians believe that it is related to too little roughage in the diet. Roughage is coarse, bulky food that is rich in plant fiber.

Down Syndrome

First and foremost, Jason's sister Anna is a happy, active, five-year-old girl. But she also is a girl with Down Syndrome, and Jason feels more protective of his sister than do most big brothers.


Don is an energetic and outgoing young man in his twenties, and when people stare he never misses the opportunity to explain that he has achondroplasia (a-kon-dro-PLAY-zee-a), a genetic condition that affects his skeletal system and causes his unusual appearance.


Dyslexia is a learning disability* that makes a person unable to recognize written words properly. It comes from the combination of two Greek words: "dys," which means trouble, and "lexia," which means words.


Annie, who had just turned 15, was running for student council treasurer. On the morning of her campaign speech before the entire student assembly, her heart began to race in her chest.