Anyone who's had chicken pox can develop herpes zoster, or shingles. The reason -- the same virus that causes chicken pox causes zoster. The virus remains in a dormant state in certain nerve cells of the body and then reactivates, causing zoster. About 20 percent of the population are affected at some time during their lives.

What prompts the virus to "awaken" and cause problems in normal, healthy people is not clear. Most physicians believe there is a temporary weakness in the body's ability to fight off disease. This allows the virus to start reproducing and move along nerve fibers toward the skin. The fact that the disease occurs more often in people older than age 50 (although children can get it, too) supports this since the immune response is believed to be weaker in older people. Trauma or possibly stress may also trigger a zoster attack.

People whose ability to ward off disease is weakened are more prone to develop zoster. They are also more likely to have a serious form of it. This includes some people with cancer, such as leukemia or lymphoma, or who have undergone chemotherapy or radiation therapy for cancer.

People who have had organ transplants and are taking drugs to ward off transplant rejection may also be more susceptible, as well as those with diseases that affect the immunological system, such as AIDS.

If someone has zoster, is there any reason to worry about a more serious disease or a poorly functioning immunological system? If you have other medical problems or could have been exposed to the AIDS virus, be sure to let your dermatologist know. Treatment of zoster would be different under these circumstances. The physician will ask questions about your medical history and may order certain tests, such as chest x-ray or blood studies, to make sure there are no other problems. The majority of people who develop zoster, however, are otherwise healthy.

Is there much scarring? Usually scarring occurs only in persons who have more severe infections, such as those with weakened immune systems or elderly persons or those with blisters become infected.

RECOGNIZING AN OUTBREAK

Early signs of a shingles outbreak are often vague, and can easily be mistaken for other illnesses.

The first sign of an attack can be an isolated pain or numbness in a major nerve in or under the skin or a "shooting" pain around the trunk or down the arm or leg. Mild flu-like symptoms, such as headache, fever and upset stomach, may also occur.

At this point, these symptoms can be confused with other illnesses, such as an ulcer, ruptured disc, pneumonia, appendicitis, or even a heart attack. but as the outbreak progresses, the symptoms become clear and the diagnosis is made more definite.

Lesions (rash) appear on the skin from one to 14 days later, usually in a band on one side of the body or back, or clustered on one side of the face. The number of lesions varies from person to person. These lesions become fluid-filled blisters in two to four days. They continue appearing for several more days, then turn from clear to cloudy in appearance as white blood cells attack the virus.

Eventually all the blisters crust, scab and heal, most often within a few weeks. Vision and hearing problems are less common, but equally serious, and can occur whenever shingles appears on the face. If this happens, you should see your doctor immediately. If shingles affects the eye, it can cause temporary or permanent blindness through infection of the cornea or retina.

Is zoster contagious?

The virus that causes zoster can be passed on to others, but they will develop chicken pox, not zoster. Zoster is much less contagious than chicken pox. Persons with zoster can only transmit the virus if blisters are broken and someone who never has had chicken pox or who already is ill is close by. Newborns or those who already are ill or immunosuppressed, such as cancer patients, are at the highest risk. Because of the risk of contagion for these people, these patients with zoster are rarely hospitalized unless absolutely necessary.

What about treatment?

In most people with zoster, the condition clears on its own in a few weeks and seldom recurs. Treatment is helpful. It usually consists of pain relievers as well as cool compresses to help dry the blisters. There are several highly effective medications for zoster. Antiviral pills (Famvir, Zovirax, Valtrex) will only work if started in the first 3 days. Others (Neurontin, Tegretol, Elavil) help the pain that may follow. Injections of cortisone, especially if directly into the area of