Once you've had chickenpox, the virus remains in your body for the rest of your life. As you age or if your immune system is suppressed, such as from medications or chemotherapy, the virus can reactivate, causing shingles.

Postherpetic neuralgia occurs if your nerve fibers are damaged during an outbreak of shingles. Damaged fibers can't send messages from your skin to your brain as they normally do. Instead, the messages become confused and exaggerated, causing chronic, often excruciating pain that can last months — or even years.

Sept. 16, 2015