The varicella-zoster virus triggers shingles in people who previously had chickenpox, Medical News Today states. After a chickenpox infection, the virus stays in the central nervous system in a dormant state for years. In some people, the virus eventually travels from nerve cells in the brain or spinal cord to other parts of the body, causing a shingles infection.
Doctors do not know exactly why the varicella-zoster virus is reactivated, but the trigger may be linked to an immune system weakness, the American Academy of Dermatology notes. A shingles infection is more likely to occur in people over age 50 and people with an injury, illness or immune system deficiency. Intense stress is also a risk factor.
Shingles typically causes red rashes that may start as blotches and turn into fluid-filled blisters, according to Medical News Today. The blisters are often clustered into bands, known as dermatomes, and commonly form around the face, waistline or one side of the trunk. Scientists believe the virus usually targets one nerve and causes inflammation along the pathway leading to the skin, which accounts for the localized rash. Shingles generally causes localized itching and shooting pain, which may include an intense stabbing sensation or a constant dull burning. The surrounding skin may also feel tender, numb or tingly.