Once someone has had a case of chicken pox, the varicella zoster virus migrates to the nerve ganglia near the spine of the patient where it enters a dormant state. The virus can reactivate after many years causing severe nerve pain and a blistering rash. Once the virus reactivates, it travels back along the sensory nerve pathways to the surface of the skin and erupts into a rash that traces the infected nerves. This skin rash typically manifests as banded in appearance, giving rise to the nomenclature of the disease. Zoster and zona are the Greek and Latin words for “girdle”, describing the belt-like appearance of the rash.

Considerable evidence exists that indicates a connection between a weakening of the immune system in the patient and the reactivation of the varicella zoster virus. The suppression of the immune system can arise from numerous factors such as fatigue, stress, chemotherapy or simple aging. Incidents of shingles are most common in older adults. There is not a clear understanding as to why a depression of the immune system causes a reactivation of the varicella zoster virus in some people but not in others. 

One cannot catch shingles from an infected person but exposure can cause chicken pox in an individual who has not previously had the varicella zoster virus. Exposure of a person who has previously had chicken pox to one who has shingles will not induce shingles in the healthy person since they already have immunity. Transmission of the varicella zoster virus from herpes zoster patients can only occur through direct contact with the fluids from the exposed lesions. Thus, one can consider shingles as contagious only between the time the blisters rupture and the time they crust over. Shingles is therefore much less contagious than chicken pox.

The nerve pain caused by shingles can persist for a considerable amount of time after the rash is resolved. Postherpetic neuralgia is the name given to this chronic pain and can last for months or even years but most commonly will subside in a matter of weeks. This complication is a result of damage to the sensory nerve pathways caused by the varicella zoster virus but rarely occurs in patients under forty years of age. Other serious complications may involve disruption of vision, hearing and balance and even encephalitis or localized paralysis, depending on which nerves are infected.