Shingles is a painful disease in which a rash with small clusters of blisters forms on the skin. It occurs chiefly among elderly persons. Shingles is caused by the varicella-zoster virus, which is one of the herpesviruses. This same virus causes chickenpox (see Chickenpox). Shingles affects persons who have had chickenpox and have developed partial immunity (resistance) to the virus. Physicians call shingles herpes zoster.