Chickenpox is caused by a virus called the varicella-zoster virus (varicella is the medical name for chickenpox).
Chickenpox is a mild but highly infectious disease that most children catch at some point. It is most common to catch the disease between March and May. It takes 10-21 days for the symptoms to show after you have come into contact with the virus. This is called the 'incubation period'.
Chickenpox is most common in children who are between two and eight years of age, although you can develop chickenpox at any age. You are infectious from about two days before the rash appears until roughly five days after. Therefore you or your child should stay at home until all of the blisters have fully crusted over, and this usually happens five to seven days after the first blister appears. After the last blister has burst and crusted over, you are no longer infectious.
Chickenpox spreads via tiny droplets of saliva and nasal mucus in sneezes and coughs from an infected person. The virus is already in these droplets, which is why it spreads so fast.
Once you have had chickenpox, you will very rarely catch chickenpox for a second time. This is because your body develops immunity to the chickenpox virus, which stops you from becoming re-infected.
Shingles
After a chickenpox infection, the virus stays in the body's nerve tissues (remains dormant). It does not do any harm because it is kept under control by the immune system, the part of the body that fights infection. At any time later in life, but usually when you are an adult, the virus can be reactivated (come back), causing a different form of the virus, known as shingles.
The first sign of shingles is usually a pain in the area of the affected nerve. Seven days later a rash will usually appear, followed by blisters, that tend to only affect one side of your body. If you have shingles you are contagious to anyone who has not had chickenpox. However, it is not possible to catch shingles from someone who has chickenpox.
Pregnancy
More than 90% of pregnant women are immune to the chickenpox virus (as a result of having it earlier on in life), so most women need not worry about developing the disease. Even if you develop shingles during pregnancy, it should not affect your baby in any way.
Chickenpox occurs in approximately three in every 1,000 pregnancies and can cause serious complications for both you and your child. Your GP will be able to advise you on any necessary tests or treatment you may require (see diagnosis and complications sections for further information).
Disease
A disease is an illness or condition that interferes with normal body functions.
Tissues
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.
Immune system
The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.
Pain
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Contagious
Contagious is when a disease or infection can be easily passed from one person to another.
