What is shingles?

A. Shingles (herpes zoster) is a common but often misunderstood condition. It’s not actually a new infection but a reemergence of the virus that causes chickenpox. Like other herpes viruses, this one never disappears from the body but lies dormant in the roots of nerves. For unexplained reasons, the virus can flare up, traveling along the nerves up to the surface of the skin. There it can cause an itchy, painful rash with blisters, and it can cause scarring. The rash has a characteristic appearance because of the structure of the underlying nerves: It’s often patchy but forms in a band, often around the torso. Flu-like symptoms are also common.

Dr. John Brusch, an infectious disease specialist at Cambridge Health Alliance, says that anyone who has had chickenpox is at risk of shingles, which includes more than 90 percent of the adult population. “Twenty percent of all people in this country will have a case of shingles in their lifetime,’’ he says. It’s most common after 50, because immunity to the virus wanes over time. Shingles is not contagious; it’s possible to cause chickenpox in a person who has not yet had it, but only with very close contact with the rash. Shingles can recur in the same person but only rarely.

Shingles is treated with antiviral medications, which are most effective if taken in the first three days, Brusch says. For that reason, he recommends seeing a doctor immediately if you suspect you might have it. “Most doctors would rather have people cry wolf about this one,’’ he says. If left untreated, shingles can cause long-term nerve pain, or neuralgia.

A vaccine (Zostavax) is now available for shingles, and is recommended for adults over 60. Brusch says that while the vaccine is not completely effective at preventing shingles, it can also make cases milder and prevent debilitating neuralgia.