Shingles (herpes zoster) is an outbreak of rash or blisters on the skin that is caused by the same virus that causes chickenpox — the varicella-zoster virus.
The first sign of shingles is often burning or tingling pain, or sometimes numbness or itch, in one particular location on only one side of the body. Shingles pain can be mild or intense.
When the varicella-zoster virus reactivates, the virus moves back down the long nerve fibers that extend from the sensory cell bodies to the skin. The viruses multiply, the tell-tale rash erupts, and the person now has shingles.
SOURCE: NINDS Shingles Information Page