The word hernia, in Latin, means rupture. A hernia refers to an opening, or separation, in the muscle, tissue, or membrane that normally holds an organ in place.


Cold sores or fever blisters—those annoying purplish-reddish-whitish blisters that tend to pop up around people's mouths—are the most familiar sign of herpes, one of the world's commonest viral infections. Its full name is herpes simplex infection, and it occurs around the globe, even among remote Indian tribes in Brazil.


Most hiccups are not harmful. The frequency of most hiccups is usually from 4 to 60 hiccups a minute.


Hives, also known as urticaria (ur-ti-KARE-e-a), develop as a reaction to various stimuli. Certain foods, food additives or dyes, drugs, alcohol, or viral infections can cause hives in susceptible people.


*parasitic (para-SIT-ik) refers to creatures that live in and feed on the bodies of other organisms.

Huntington's Disease

In the United States, only about 5 out of 100,000 people develop Huntington's disease. Because it is transmitted from parent to child, only children of a parent who has the abnormal gene are at risk, and they have a 50 percent chance of developing the disease.


When Liz saw her baby brother in the hospital nursery, she was upset by his appearance. His head seemed huge.


Hypertension is the medical term for high blood pressure. Arteries are the blood vessels that carry the blood from the heart through the entire body.


Researchers say that between 4 and 9 percent of visits to physicians involve people with hypochondria. These people say that they feel sick and often have detailed explanations for their beliefs.


Melinda was at the mall with friends, when she started to feel weak and uncoordinated. She developed a pounding headache, began to shake and sweat, and could not see very well.


The immune system, which protects the body from disease, works through a complicated web of cells and chemicals. It has many intertwined parts.


Older men and women, as well as some young children, find they cannot wait when they have to go to the bathroom. Usually, incontinence (in-KON-ti-nens) involves urinating at the wrong time, or it can mean having a bowel movement before reaching a bathroom.


Organisms that can cause illness are all around us: in air, water, soil, and food, as well as in the bodies of animals and other people. Infection occurs when some of them get past a series of natural defenses.


Infertility is defined as the failure to become pregnant after about a year of trying many times without using contraception*. Infertility problems increase as a person gets older, and they are becoming more widespread as many women are waiting to have babies until they are in their thirties and forties.

Inflammatory Bowel Disease

*inflammation (in-fla-MAY-shun) is the body's reaction to irritation, infection, or injury that often involves swelling, pain, redness, and warmth.


Joseph is not feeling well, but he goes to school anyway. He is coughing, sneezing, and starting to feel very tired.

Ingrown Toenail

An ingrown toenail is a common condition in which the corners or sides of the toenail cut into the skin of the toe. This usually happens to the big toe, and can affect people of all ages.


Humans, like all earth's creatures, have cycles of activity and rest, which perhaps evolved partly as a response to the cycles of night and day. Many of the body's hormones* and processes are related closely to such daily cycles.

Irritable Bowel Syndrome

Playing the flute was Georgia's favorite activity. When she got to college, Georgia majored in music and performed regularly with the college orchestra.


When a person is in good health, the bile pigment* bilirubin is formed from the normal breakdown of hemoglobin (HE-mo-globin), which is the oxygen-carrying substance in red blood cells. This process occurs naturally as old red blood cells wear out and are replaced in the body.

Jet Lag

Jet lag is a common affliction that has surfaced in recent years. The body's internal clock is "set" for the time zone in which a person lives.

Kidney Cancer

The kidneys are two bean-shaped organs located near the spine whose main function is to filter salts, excess water, and impurities from the blood, producing the liquid waste called urine. Urine drains from the kidneys to the bladder through a tube called the ureter.