Herpes Zoster, also known as shingles or zoster, is a viral infection caused by the same virus that causes chicken pox. Anyone who has had chicken pox can develop herpes zoster. The virus remains dormant (inactive) in certain nerve cells of the body, and when it reactivates it causes zoster. About 20 percent of those people who have had chicken pox will get zoster. Most people get zoster only once.
It is not clear what makes the virus reactivate or "awaken." A temporary weakness in immunity (the body's ability to fight infection) may cause the virus to multiply and move along nerve fibers toward the skin. Although children can get zoster, it is more common in people over the age 50. Illness, trauma, and stress may also trigger zoster.
People with a weakened immunity for any reason like cancers, leukemia or lymphoma, or AIDS are prone to developing zoster. Medical treatments like chemotherapy or radiation for cancer, drugs taken to prevent rejection of transplanted organs, and cortisone taken for a long time, can make someone susceptible.