Postherpetic neuralgia is a painful condition affecting your nerve fibers and skin. It's a complication of shingles, a second outbreak of the varicella-zoster virus, which initially causes chickenpox.

During an initial infection of chickenpox, some of the chickenpox virus can remain in your system, lying dormant inside nerve cells. Years later, factors such as age, illness, stress or medications can reactivate the virus. It can also reactivate for no apparent reason.

Once reactivated, the virus travels along nerve fibers, causing pain. When the virus reaches the skin, it produces a rash and blisters, known as shingles (herpes zoster). A case of shingles usually heals within a month. But some people continue to feel pain long after the rash and blisters heal. This pain is known as postherpetic neuralgia.

Prevention

In 1995, the Food and Drug Administration (FDA) approved the vaccine Varivax to prevent chickenpox. Its effect on postherpetic neuralgia is unknown. The vaccine — made from a weakened form of the varicella-zoster virus — may keep chickenpox from occurring in nonimmune children and adults, or at least lessen the risk of the chickenpox virus lying dormant in the body and reactivating later as shingles. If shingles could be prevented, postherpetic neuralgia could be completely avoided.

If you've already had chickenpox, the vaccine can't prevent shingles because the varicella-zoster virus is already in your body.