Herpes zoster or shingles is a painful skin rash involving blisters which is caused due to caricella-zoster virus. This virus also causes chicken pox. Once you contract chicken pox, the virus becomes dormant in some nerves of your body. Herpes zoster occurs when the virus in the nerves becomes active again later on. The reason why the virus becomes active again is unknown.The first symptom experienced is one-sided pain, burning or tingling. There may be severe pain and burning present before any rash appears. It is then followed by red patches on the skin and formation of small blisters.