Shingles is a reactivation of the herpes zoster virus (varicella-zoster virus, or VZV). This same virus causes the childhood illness chickenpox. The chickenpox virus (varicella) remains in a dormant state in the body in the root of nerves that control sensation. In about 1 out of 5 people, the virus "wakes up," often many years after the chickenpox infection. The virus then travels along a sensory nerve into the skin causing a painful rash known as shingles.
Shingles is derived from the Latin and French words for belt or girdle, reflecting distribution of the rash in a broad band. This band is usually only on one side of the body and represents a dermatome—the area that a single sensory nerve supplies in the skin.
Anyone who has had the chickenpox infection or vaccine can get the herpes zoster virus that causes shingles. Older people and those with cancer, HIV, or organ transplants have a decreased ability to fight off infection and a greater chance of getting shingles.
The majority of people with shingles, however, are healthy. No special tests need to be done to see if your immune system is strong.