Definition of Herpes zoster:

Herpes zoster (shingles) is a painful, blistering skin rash due to acute infection with the varicella-zoster virus, the virus that causes chickenpox.

See also: Ramsay Hunt syndrome

Causes, incidence, and risk factors:

After you get chickenpox, the virus falls asleep (becomes dormant) in certain nerves the body. Shingles occurs after the virus becomes reactive in these nerves after many years.

The reason the virus suddenly become active again is not clear. Often only one attack occurs.

If an adult or child is exposed to the herpes zoster virus and has not had chickenpox as a child or received the chickenpox vaccine, a severe case of chickenpox may develop, rather than shingles.

Herpes zoster can be contagious through direct contact in an individual who has not had chickenpox, and therefore has no immunity. Herpes zoster may affect any age group, but it is much more common in adults over 60 years old, in children who had chickenpox before the age of one year, and in individuals whose immune system is weakened.