What causes the reactivation of the virus is not known. A weakened immune system seems to allow reactivation of the virus. This may occur with immune-suppressing medications, with another illness, or after major surgery. Advancing age, chronic use of cortisone-type drugs, and the stress of major surgery may trigger shingles. The virus may also become active again after trauma to the skin from injury or sunburn.
Emotional stress seems to be a common trigger as well.
The first sign of shingles is often burning, sharp pain, tingling, or numbness in or under your skin on one side of your body or face. The most common site is the back or upper abdomen. You may have severe itching or aching rather than pain. You also may feel tired and ill with fever, chills, headache, and upset stomach. After several days, you will notice a rash of small, clear, fluid-filled blisters on reddened skin.