Athlete's Foot

The human body is home to many different kinds of fungi. Most never cause a problem.

Attention Deficit Hyperactivity Disorder (ADHD)

Justin and Katie are both seventh-grade students with ADHD. They act quite differently at school, however.


Like many children with autism, Jamie was concerned with order. Even as a young child, he kept his toys in the exact same spot on his shelves and would become very angry if anything was moved.


Watch out for that tick! Ticks carry many different diseases, including babesiosis (ba-bee-ze-O-sis), Lyme disease, and Rocky Mountain spotted fever.

Bacterial Infections

Bacteria are everywhere: in soil, in water, in air, and in the bodies of every person and animal. These microorganisms* are among the most numerous forms of life on Earth.

Bedsores (Pressure Sores)

Bedsores develop when the skin is compressed between a protruding bone, like a hipbone or elbow, and an external surface, like a wheelchair or mattress, over a long period of time. This compression limits the flow of blood in blood vessels that bring nutrients and oxygen to the skin and remove wastes.

Bedwetting (Enuresis)

Bobby felt ashamed when he woke up and discovered his underwear and bed sheets were wet again. He had urinated while sleeping.

Bell's Palsy

Fifteen-year-old Shelly woke up one morning feeling like she had just received a shot of Novocain from the dentist. When she looked in the mirror, she saw that her face seemed limp on one side.


The bends is also called decompression sickness or caisson* sickness. When a person is scuba diving, the water pressure increases with depth.

Birth Defects

A birth defect is an abnormality in the body structure or chemistry of a newborn child. It may be caused by hereditary factors (that is, by genetic causes), by environmental influences that affect the embryo or fetus in the mother's womb, or by a combination of factors.

Bites and Stings

In addition to bites by mammals such as dogs, cats, and humans, many other animals can bite or sting people. Some animals inject venom, which is a poisonous substance, into the skin when they bite.

Bladder Cancer

Cigarette smoking is most commonly associated with lung cancer, but smokers also are two to three times more likely than nonsmokers to develop bladder cancer. Cigarette smoke contains harmful cancer-causing chemicals called carcinogens (kar-SIN-o-jenz).


Corrine tried to imagine how she would describe a bird to her sister Amy, who might never be able to see one. She could say that it is small, that it has feathers, and that it sings.


"I'll have a patty melt on toasted rye, with American cheese and sautéed onions." With those words, 28 patrons in a Peoria, Illinois, restaurant unknowingly exposed themselves to botulism. Without seeing, tasting, or smelling anything unusual, they ate a toxin produced by bacteria spores growing on the onion skins.

Brain Tumor

A brain tumor is a clump of abnormal tissue that can be found anywhere in the brain. The brain and spinal cord form the central nervous system, which controls everything a person does on purpose (such as walking and talking), or automatically (such as breathing and digesting food).

Breast Cancer

In the United States, breast cancer is a very common cancer among women, second only to skin cancer. Breast cancer also occurs in men, but much more rarely.

Broken Bones and Fractures

Ken knew the steps to the attic were steep, but when his little sister ran off with his toy airplane, he took the stairs two at a time. Halfway down he slipped.


Chrissy's father had been smoking cigarettes since he was Chrissy's age. In the last few years, though, her father had developed a nasty cough that never seemed to go away.


When Natalie began her job at the bank, she finally could afford to indulge her love of stylish shoes. The higher the heel and the pointier the toe, the better.


The skin is the protective outer surface of the body. Its outer layer is the epidermis, comprising several layers of epithelial cells arranged like shingles on a roof.


Campylobacter (kamp-pi-lo-BAK-ter) is a type of bacteria that is a normal inhabitant of the digestive tract of many animals. People, however, do not normally carry Campylobacter, and exposure to it usually causes an intestinal infection called campylobacteriosis (kamp-pi-lo-bak-ter-ee-O-sis).


The disease we call cancer has been around as long as we have. Evidence of cancerous growths, or tumors, has been found among fossilized bones and in human mummies dating from ancient Egypt.