//// Shingles is a reactivation of the varicella zoster virus infection that causes chickenpox. After a person has had chickenpox the virus remains in their body, lying dormant or hidden in part of the nervous system.
For some reason, often many years later, the virus travels back down one of the nerves to the skin, where it causes a rash in the area of skin supplied by that nerve.
It's not clear what triggers reactivation of the chickenpox virus but it may be linked to changes in the immune system such as an infection elsewhere in the body, or after physical or emotional shock. Ensuring your immune system is not weakened may help to prevent this occurring.
Around one in four people will develop shingles in their lifetime, with men and women affected equally. It's most common in older people, although it can also occur in younger people and those with a weakened immune system.
The skin blisters that form in shingles are full of the chickenpox virus, which means a person with shingles is infectious. You can catch chickenpox from someone with shingles, if you've never had the infection and therefore aren't immune. But you can't catch shingles from someone with shingles (or someone with chickenpox).
Most adults - about 95 per cent - have been exposed to chickenpox and are immune, even though many aren't aware of it (they may have had only a mild dose of chickenpox when they were young). However, a small number of adults aren't immune and will be at risk. Also, when the immune system is suppressed (for example, when someone is being treated for cancer), a person can catch chickenpox for a second time. ////
http://www.bbc.co.uk/...tions/shingles1.shtml