Post-herpetic neuralgia (PHN) is a chronic pain disorder that occurs as a complication of shingles, a viral infection caused by the varicella-zoster virus. Shingles is an infection of a nerve and the surface of the skin supplied by that nerve, causing a severely painful rash, blisters and flu-like symptoms. After the shingles rash has resolved, some people may continue to experience pain, numbness or tingling in the affected area; this condition is called post-herpetic neuralgia. The pain can range from mild to severe and last for weeks, months or even years. PHN is more common in older adults, people with weakened immune systems, and people who have had shingles before.