http://www3.niaid.nih.gov/healthscience/healthtopics/shingles/
National Institute of Allergy and Infectious Diseases, National Institutes of Health
Shingles is caused by the varicella-zoster virus, the same virus that causes chickenpox. After an attack of chickenpox, the virus lies dormant in the nerve tissue. As we get older, it is possible for the virus to reappear in the form of shingles. Shingles is estimated to affect 2 in every 10 persons in their lifetime. This year, more than 500,000 people will develop shingles.