What exactly are shingles and once contracted can they reoccur?

Shingles ( zoster) is caused by the reactivation of the virus that causes chickenpox. After you recover from chickenpox, the virus lies dormant (inactive) in your nerve roots. In some people, it stays dormant for the rest of their lives. In others, the virus reactivates when disease, stress, or aging weakens the immune system. The cause of reactivation of the virus is unclear; however, once it does reactivate, it causes shingles, not another case of chickenpox. Most people who get shingles will not get the disease again, although it does come back in a few people.