Shingles, also known as herpes zoster, is a viral infection which causes an extremely painful rash. Although shingles can occur anywhere on your body, it most often appears as a cluster of blisters that wraps from the middle of your back around one side of your chest to your breastbone, following the nerve roots of the spine.

Shingles is caused by the Varicella zoster virus, the same virus that causes chickenpox. Once you’ve had chickenpox, the virus lies dormant in nerve tissue near your spinal cord and brain; years later, the virus may reappear as shingles. Although V. zoster is part of a group of viruses called herpes viruses which includes the viruses that cause cold sores and genital herpes, it does not cause these diseases.

The symptoms of shingles may include pain (usually the first sign), burning, numbness or tingling. A red rash begins a few days after the onset of pain and develops into fluid-filled blisters that break open and crust over. Patients complain of itching; some also experience fever and chills, general achiness, headache and fatigue. For some, the pain can be intense, feeling at times like a twisting knife. Depending upon the location of the pain, it can sometimes be mistaken for a symptom of heart, lung or kidney problems. Some people experience shingles pain without ever developing the rash. Sometimes the shingles rash occurs around one eye or on one side of the neck or face.

Doctors are not sure how or why the V. zoster virus reactivates. They believe that the immune system’s response to the virus weakens over the years after childhood chickenpox. Anyone who has ever had chickenpox can develop shingles, but it is most common in adults over the age of 50 and in people who have weak immune systems. Most adults in the United States had chickenpox when they were children, before the advent of the routine childhood vaccination that now protects against chickenpox. Shingles risk increases with age, and some experts estimate that half the people who live to the age of 85 will experience shingles.

People with weakened immune systems are at higher risk for developing shingles. A weakened immune system can be caused by HIV/AIDS, cancer or cancer treatments, prolonged use of steroids and drugs designed to prevent rejection of transplanted organs.

A person with shingles can pass the V. zoster virus to anyone who has not had chickenpox. This usually occurs through direct contact with the open sores of the shingles rash. Once infected, however, that person will develop chickenpox, not shingles. Chickenpox can be dangerous for some groups of people. Until your shingles blisters scab over, you are contagious and should avoid physical contact with newborns, pregnant women or anyone who has a weak immune system.

Complications from shingles can range from mild (minor skin infections) to severe (post-herpetic neuralgia — when shingles pain continues long after the blisters have cleared). Shingles in or around an eye (ophthalmic shingles) can cause eye infections that may result in vision loss. Depending upon which nerves are affected, shingles can cause nerve problems such as encephalitis (inflammation of the brain), hearing or balance problems and facial paralysis. If shingles blisters aren’t properly treated, bacterial skin infections may develop.

Contact your doctor promptly if you suspect shingles, but especially if the pain and rash occur near your eyes, if the rash is widespread and very painful or if you or someone in your family has a weakened immune system.

Shingles is usually diagnosed based on the history of pain on one side of your body, along with the telltale rash and blisters. Your doctor may also take a tissue scraping or culture of the blisters for laboratory examination.

An episode of shingles usually heals within a few weeks to months, but prompt treatment can ease pain, speed healing and reduce your risk of complications. For best results, start antiviral medications within 72 hours of the first sign of the rash. Shingles can cause severe pain, so you may need prescription medications which may include narcotics, tricyclic antidepressants, anticonvulsants or numbing agents applied to the skin.

Depending on your level of pain, you might not feel like doing much, and you may feel weak and tired. Be sure to get plenty of rest and avoid strenuous activities. Also avoid stress, which can worsen pain. Relaxation techniques, including listening to music or deep breathing, might help. Taking a cool bath or using cool, wet compresses on your blisters may relieve the itch and pain. Over-the-counter medications may help, such as pain relievers or anti-itch medications (such as Benadryl).

Two vaccines can help reduce the risk of shingles: the chickenpox (Varicella) vaccine and the shingles (V. zoster) vaccine. If you’re younger than 60, hold off on the shingles vaccine until you reach that age. Children and adults who have not had chickenpox should receive the chickenpox vaccine instead. For more information, visit www.cdc.gov.