Shingles is caused by the same virus that causes chickenpox.
After you have chickenpox, the virus that caused it, called varicella, remains in your body. It's always inside you, lying dormant (or asleep) in your nerve cells. At some point later in life, your immune system may weaken, allowing the virus to resurface as Shingles. You may be feeling great, but if you've had chickenpox, the Shingles virus is already inside you. And your risk for Shingles increases as you get older.
The Shingles rash usually affects only one of the parts of the body shown below.
Most often, the Shingles rash occurs in a band or strip on one side of the body. This band is called a dermatome, which is the area where one of the nerves from your spinal cord connects with the skin. Shingles usually appears along a dermatome, each of which is located on one side of the body. Shingles may also appear on a single side of the face, for example, in the area around the eye and the forehead. But Shingles can strike any dermatome on the body.