Shingles (herpes zoster) is a viral infection caused by varicella-zoster virus (VZV), the same virus that causes chickenpox. After a person has had chickenpox, VZV remains in a dormant (inactive) state in the nerve roots for the remainder of their life. VZV may re-activate itself years later in the form of a painful skin rash known as shingles.  More than 500,000 cases of shingles are reported annually in the United States, according to the National Institute of Allergy and Infectious Diseases. About 20 percent of patients who have had chickenpox will develop shingles in their lifetime.

A rash usually appears about two to three days after VZV has become active in the nerves and reached the skin of the affected area. Why VZV emerges from dormancy is unknown, though it may occur in relation to a number of factors (e.g., stress, impaired immune system). The rash consists of small red blisters (vesicles) that resemble the early stages of chickenpox. It may spread over the next three to five days to include a larger area of the body.

Rash blisters or lesions most often appear along a single dermatome (a segment of the skin supplied by specific spinal nerves) and on only one side of the body. Occasionally two or three adjacent dermatomes may be involved. The thoracic (chest) and lumbar (lower back) dermatomes are most often affected by shingles. Rarely, a patient may experience pain but not the appearance of shingles itself (zoster sine herpete).

Repeated attacks of shingles are possible. However, most episodes are mild and occur once, unless the patient is immunosuppressed (e.g., HIV patient, organ transplant recipient, chemotherapy patient). Widespread or recurrent shingles may indicate an underlying problem with the immune system. Shingles most often affects adults of both genders aged 55 and older. This may be due to a breakdown in VZV immunity as people age. However, shingles may potentially affect anyone infected with VZV due to an earlier chickenpox infection. A fetus that is infected with chickenpox while in the womb can go on to develop shingles as an infant.

Some people may experience post-herpetic neuralgia, a condition that causes the skin to remain painful for months or sometimes years after a shingles rash has gone away. Post-herpetic neuralgia pain can be slightly uncomfortable or severe and incapacitating, resulting in depression, anxiety and sleeping difficulties. The rate of incidence increases significantly with age, usually occurring in patients aged 60 and older. It is also more common in those with facial infection.

Rarely, other potentially serious complications may occur in association with shingles, including:

• Bacterial skin infection
  
  
• Inflammation of the cornea (keratitis) or membranes of the eye (uveitis)
  
  
• Nerve damage
  
  
• Meningitis (inflammation of the membranes that protect the brain and spinal cord)
  
  
• Encephalitis (inflammation of the brain)
  
  
• Stroke
  
  
• Myelitis (inflammation of the spinal cord)