Shingles is a viral infection caused by the varicella-zoster virus, the virus that also causes chickenpox. It belongs to a group of viruses called herpes viruses which are responsible for cold sores and genital herpes. With shingles, a painful rash with blisters similar to cold sores forms on the skin, usually in a strip that wraps around half of the torso on either the left or right side. Occasionally people will get this rash on one side of the neck or around one eye. The fluid-filled blisters are painful, sensitive to touch, can open and crust over, itch, burn, or cause numbness and tingling. Generally, the pain from shingles is felt before the rash arrives and can be accompanied by fever, headache, fatigue, and sensitivity to light. Some people may feel the pain, but never get the rash.

After recovering from chickenpox, the virus enters the nervous system and lies dormant in nerve tissue near the brain or spinal cord. When the virus reactivates in the body, usually in older adults (over 50) and those with weakened immune systems, it comes back as shingles. Complications that can arise from the infection are: postherpetic neuralgia in which damaged nerve fibers continue to send pain signals to the brain after the blisters have healed, vision loss from eye infections from blistering around the eye, skin infections from open blisters that are not properly cared for, and neurological problems like encephalitis (inflammation of the brain), facial paralysis, hearing problems, or balance issues.

Shingles is contagious until the point when the blisters have scabbed over (2 to 6 weeks) and can be spread to those who are not immune to chickenpox (although they would get chickenpox, not shingles). There is no cure, but antiviral drugs given early in the infection can increase healing time and decrease the risk of further complications. For pain, doctors may prescribe anticonvulsants, narcotics, lidocaine, capsaicin patches, or corticosteroid injections.