Postherpetic neuralgia (PHN) is a complication of shingles infection (also called herpes zoster). Shingles is caused by the reactivation of the varicella-zoster virus, which is the same virus that causes chickenpox. Shingles causes a painful, blistering rash and other symptoms. The rash most commonly occurs in a band pattern on one side of your body, usually on your trunk (central core of your body). The rash turns into blisters. As the rash/blisters go away, pain may remain. When pain remains, the condition is called postherpetic neuralgia.