Shingles is an infection of a nerve and the area of skin supplied by the nerve. It is caused by a virus called the varicella-zoster virus. It is the same virus that causes chickenpox. Anyone who has had chickenpox in the past may develop shingles.

About 1 in 5 people have shingles at some time in their life. It can occur at any age, but it is most common in people over the age of 50. It is uncommon to have shingles more than once, but about 1 in 50 people have shingles two or more times in their life.

How does shingles occur?

Most people have chickenpox at some stage (usually as a child). The virus does not completely go after you have chickenpox. Some virus particles remain dormant (inactive) in the nerve roots next to your spinal cord. They do no harm there, and cause no symptoms. For reasons that are not clear, the virus may begin to multiply again (reactivate). This is often many years later. The 're-activated' virus travels along the nerve to the skin and causes shingles.

In most cases, an episode of shingles occurs for no apparent reason. Sometimes a period of stress or illness seems to trigger it. A minor 'ageing' of the immune system may account for it being more common in older people. (The immune system keeps the virus dormant and prevents it from multiplying. A slight weakening of the immune system in older people may account for the virus 'reactiving' and multiplying to cause shingles.)

Shingles is also more common in people with a poor immune system. For example, shingles commonly occurs in younger people who have HIV/AIDS or whose immune system is suppressed with treatment such as steroids or chemotherapy.

- Read more: what are the symptoms of shingles?

More help and advice

- Expert advice on shingles
- How to relieve the pain of shingles
- Read Joanne's story: 'A jabbing pain turned out to be shingles'
- Check out the full facts about chickenpox

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