Shingles are caused by varicella-zoster, the same virus that causes chickenpox. If you've ever had chickenpox (typically during childhood), this virus is quietly hiding out in the roots of your nerves. It can reactivate and cause a painful skin rash. This is known as shingles or herpes zoster.
Not everyone who has had chickenpox will develop a case of shingles. Approximately 20% of North Americans develop shingles at some point in their life. Most people who get shingles are 50 to 70 years of age, but it can happen at any age.
The latent or "quiet" infection caused by varicella-zoster can become active again, even many years after you've had chickenpox. This can occur when your immune system isn't working at its best. This may be due to any of the following reasons:
Most of the time, it is difficult to know exactly what triggered reactivation of the virus. Shingles rarely occur in children under the age of 10. The risks of getting it at that age increase significantly if a child has been infected with the virus during the first year of life, or if the mother had chickenpox during pregnancy.
A person with a shingles rash can pass the varicella-zoster virus onto someone who has not yet been infected with the virus, usually a child. However, the newly infected person would develop chickenpox, not shingles. Shingles occurs as a reactivation of the latent virus, not from "catching it" from someone who has shingles.
When the virus becomes active again, you may get symptoms such as rash, upset stomach, headache, fever, and chills. These symptoms are often preceded by warning signs (the prodrome) such as sensitivity, itchiness, numbness, or pain in the days before the rash appears. The rash produces painful, fluid-filled blisters, and you'll feel tingling or burning sensations.
When the varicella-zoster virus enters its "quiet" phase after chickenpox, it remains dormant in certain nerves. The shingles rash will break out in the areas of the body connected to those nerve cells. As a result, only one section or one side of the body is often affected. Common sites for the rash include the chest, back, buttocks, neck, and sometimes the face and scalp.
The rash itself is reddish, with many tiny, fluid-filled blisters. For a few days, the rash spreads, although its extent varies from one person to another. The rash commonly occurs on one side of the trunk of your body as a band of blisters that go from the middle of your back around one side of your chest to your breastbone. The blisters will break, dry out, and then crust over.
From before the time the rash erupts until after it's healed, you'll be itchy - in some cases, the rash can be extremely painful. The rash usually lasts about 7 to 10 days and completely disappears after one month. The pain can last for up to 3 months or longer in a very small percentage of people. While you will likely have only one bout of herpes zoster, some people may get it several times.
If your immune system isn't working at full capacity, your rash and symptoms will be more severe and take longer to heal, which can lead to scarring. The virus can also spread to other organs in your body, but this is rare for people with healthy immune systems.
Post-herpetic neuralgia (PHN) is one of the complications of shingles. It is characterized by severe pain along affected nerves where the herpes zoster virus is located. It can last for several weeks, months, or years, and can be permanent. The cause of PHN is not known.
Other complications can occur if the virus spreads up the nerve that connects to your eyes. This may result in an eye infection or eye pain triggered by exposure to light. Your eye doctor should be consulted immediately if shingles in the eye area is suspected. If left untreated, the virus can cause blindness. If the virus spreads to two particular nerves in your face, then a condition called Ramsay Hunt syndrome can develop. This can lead to temporary ear pain, facial paralysis, and loss of hearing and taste.