Shingles is a reactivation of the varicella-zoster virus, a type of herpes virus that causes chickenpox. After you have had chickenpox, the virus lies inactive in your nerve roots and remains inactive until, in some people, it flares up again. When the virus becomes active again, you get shingles instead of chickenpox.

Anyone who has had even a mild case of chickenpox can get shingles. People who have a weak immune system are vulnerable to reactivation of the virus that causes shingles. Many factors can weaken your immune system, including aging, injury, and illness. Some medicines slow down the immune system. For example, medicines that destroy cancer cells (chemotherapy) can interfere with the immune system.

Transmission

Exposure to shingles will not cause you to get shingles. But if you have not had chickenpox and have not gotten the chickenpox vaccine, you can get chickenpox if you are exposed to shingles. Someone with shingles can expose you to chickenpox if you come into contact with the fluid in the shingles blisters. If you cover the shingles sores with a type of dressing that absorbs fluid and protects the sores, you can help prevent the spread of the virus to other people.