Canker Sores (Aphthous Ulcers)

Ashley first noticed a slight tingle in her mouth one morning as she was brushing her teeth before school. It was inside her lower lip, on the soft, fleshy part in front of her bottom teeth.

Carbon Monoxide Poisoning

The neighbors could set a clock by Dr. Smith's morning routine.

Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) occurs when the median nerve in the wrist is compressed by other structures in the "tunnel" formed by ligaments* and the carpal (or wrist) bones. The median nerve provides feeling to the palm, thumb, and middle fingers, and irritation of this nerve causes numbness, weakness, and pain.

Cat Scratch Disease

Bartonella henselae, the bacterium that causes cat scratch disease, is found all over the world. Cats and kittens carry the bacterium in their saliva.


Many people who live to an old age will develop cataracts, often without noticing the effects until they are past age 70. For some, it might mean only a slight change in vision.


Michael's friend Ashley always said that she loved his smile, and Michael wanted to keep it that way. However, Michael was unaware that he had a small cavity starting in one of his front teeth.

Cerebral Palsy

Rob and Carol were the first to notice that something was wrong with their eleven-month-old daughter Nancy. Nancy was an alert, happy baby.

Chagas' Disease

Chagas' disease is an infection with a protozoan (pro-to-ZO-an), a tiny parasite called Trypanosoma cruzi. This parasite infects many kinds of mammals in South and Central America.


With its rash and fever, chickenpox is common in children and usually mild. But it can be serious, especially in infants, adults, and people with weak immune systems*.

Chlamydial Infections

In the United States, Chlamydia trachomatis (tra-KO-ma-tis) is responsible for more cases of sexually transmitted diseases (STDs) than any other organism. Sexually transmitted diseases are passed from one partner to another during sexual activity.


In January 1991, an outbreak of cholera, a disease that can cause life-threatening diarrhea, began in several towns along the seacoast of Peru. Within months, the disease had spread to many countries in Central and South America.

Chronic Fatigue Syndrome

In November 1996, the enormously popular American jazz pianist Keith Jarrett found himself completely drained of energy in the middle of a concert tour in Italy. The only way he could get through his performances was to stay in bed most of the day and get up just for the concert at night.

Cirrhosis of the Liver

Many people believe that only heavy drinkers can get cirrhosis of the liver. Although it is true that the number one cause of cirrhosis in the United States is drinking alcohol, a person need not be a heavy drinker to get the disease.

Cleft Palate

Tonya and Phil were excited to hear their newborn son's first cry, but they were shocked when they saw him for the first time; baby Philip's upper lip was split up the middle. The doctor told them that Philip had a cleft palate as well as a cleft lip, and that both are fairly common birth defects.


Almost as soon as blood starts to flow from a cut finger or scraped knee, platelets begin to gather. Platelets are clear blood cells that start the process of clotting.


A virus is the smallest type of infectious agent. It is anywhere from one-half to one-hundredth the size of the smallest bacteria.

Cold-Related Injuries

Anyone who spends time outdoors in cold weather can be at risk for cold-related injuries. That includes people who fish, hunt, or hike, especially in the mountains, where temperatures can drop quickly and icy rain or snow can blow in with little warning.


Colitis is a type of inflammatory* bowel disease that affects mainly the large intestine and the rectum*. Different types of colitis may be chronic or acute and may have different causes, but they have many symptoms in common, including diarrhea that may be bloody.

Collagen Vascular Diseases

Collagen vascular diseases have been recognized for a long time. Rheumatoid arthritis is a chronic inflammatory* disease that causes stiffness in the joints (places where bones meet), and can lead to disfigurement.

Color Blindness

Red means stop. Green means go.

Colorectal Cancer

In October 1998, New York Yankees outfielder Darryl Strawberry went to see his doctor because of pains in his stomach. Surprisingly, the cause turned out to be colon cancer.


Most people who watch sporting events on television have seen team physicians run out to the playing field to examine athletes who receive blows to the head. The doctors often ask the injured players if they know where they are or what day of the week it is.