Q. Please explain "shingles." How do you get it and why does it hurt so much? Mine was on the right side of my ribcage. My doctor gave an injection and Percodan for pain, but I'm into my fourth week of "nerve pains" now. How much longer will it continue?

A. Shingles (from the Latin word cingulus, meaning belt) is a painful nerve and skin infection caused by the varicella-zoster virus, a member of the herpes family. Shingles is also known as herpes zoster or, simply, zoster, which also means belt.

Shingles gets its name from the pecular belt or band of red blistered skin that typically circles one side of the chest, though it can also break out on the face, arms or legs.

Like the herpes virus that causes fever blisters on the lips or genital ulcers, the varicella-zoster virus can invade nerve cells, lie dormant, and erupt years later in an attack of shingles.

Surprisingly enough, shingles seems to be a flare-up in adults of the childhood varicella-zoster infection we all know as chicken pox.

Most of the time it's not clear what sets off an attack, though in some people it seems to be related to weakened bodily defenses or underlying disease.

The infection almost always occurs just once, breaking out on the skin surface in a path above the affected nerve. Shingles isn't contagious between most adults, but it can cause chicken pox in youngsters.

There's no proven therapy for shingles, though preliminary studies show that the antiherpes drug acyclovir (Zovirax) taken by mouth or intravenously may be helpful in severe cases.

The skin sores usually last a couple of weeks and the nerve pains up to a month or so, though in some people they persist for many months, even years. The pain can be fairly resistant to treatment, but may respond to carbamazepine (Tegretol), phenytoin (Dilantin) or amitriptyline (Elavil).

Especially in older people, shingles can trigger persistent nerve pains even after the skin infection clears up. Some doctors try to prevent this by prescribing a cortisone-type medicine, such as prednisone, early in the outbreak. Also, preliminary studies show that the antiherpes drug acyclovir (Zovirax) taken by mouth or intravenously may be helpful in treating shingles.

The skin sores usually last a couple of weeks, and the pain up to a month or so, though in some people it persists for many months, even years. In these cases, injecting an anesthetic into the nerve may give some relief.

Q. All of my fingernails have gradually developed vertical ridges. What causes this? Also, what causes white horizontal lines on fingernails?

A. There is a saying in medicine that the skin mirrors the health of the body, and to some degree, so do your fingernails.

Horizontal white lines or bands running across your fingernails may occur for no apparent reason, but they also develop during times of general illness, such as prolonged high fevers, pneumonia or episodes of heart or kidney failure.

The lines date the period of illness, much as geological layers date a period of history, and grow out as the nail grows.

White bands under the nails sometimes develop during periods of poor nutrition. Because they're in the nail bed, and not the nail itself, they don't move forward as the nail grows.

Scattered white marks on the nails are of no special significance.

Vertical ridges running from the base of the fingernail to the tip have no apparent link to illness. Known as reedy nails, their cause is unknown, but they seem to be an accentuation of the longitudinal ridges normally present.

Q. I had several fibroid tumors removed from my uterus, one year after having a baby by cesarean delivery. My doctor told me that our next child would also have to be by cesarean birth, because my uterus might not hold up under the pressure of labor and delivery. Is this the general consensus or could I find a doctor who would allow me to have a vaginal delivery?

A. The major obstacle to a vaginal delivery in your case is not your previous cesarean birth, but your fibroid surgery. After many years, the medical teaching "once a cesarean, always a cesarean" no longer holds true.

Up to three out of four women who have what's known as a low horizontal scar on their uterus from a prior cesarean birth can later have a safe and successful vaginal delivery. Most cesarean births now performed use this type of incision in the uterus.

The American College of Obstetricians and Gynecologists recently issued guidelines about vaginal delivery after a previous cesarean birth. In brief, the guidelines are:

* The woman and her physician should fully discuss the potential risks and benefits of attempted vaginal delivery.

* Women who had a previous vertical incision in the uterus should not go into labor; they should have a repeat cesarean birth. (A vertical scar is more likely to rupture under the stress of labor).

* There should be only one baby, with an estimated weight less than 4,000 grams (8 3/4 pounds).

* Instruments that check the heart rate and well-being of the fetus during labor should be used, and staff and facilities needed for obstetric emergencies should be available.

If your surgery for fibroid tumors required cutting through the uterus (and not just removing a tumor attached by a stalk), I think most physicians would recommend cesarean birth for your next child.