ChickenpoxChickenpox is usually a mild disease. Most children catch chickenpox before the age of five and 90% have had it by the age of ten.
The incubation period (the time from contact with someone with the illness to the first signs of developing the disease) is usually 14-17 days, though may be as long as three weeks.
It is very infectious and spreads easily from child to child. The rash is often the first sign of the illness, though this may follow a day or two of feeling unwell with a temperature. The rash is unlike that in other common infectious diseases: it consists of small itchy blisters all over the body, but concentrated on the chest, tummy and back. The blisters crust and heal over a period of about a week, only rarely leaving a permanent scar, usually as a result of overenthusiastic scratching. The vast majority of sufferers are only mildly ill and make a complete recovery. Adults with chickenpox are generally more unwell than children, and also more prone to complications. The most common complication of chickenpox is skin infection, especially after lots of scratching; this may require antibiotics. Other problems are rare in children with a healthy immune system but include pneumonia (more common in adults); encephalitis (infection of the brain) from which full recovery is usual; arthritis; kidney or liver infection.
An infection usually provides life-long protection and it is rare to get a second attack of chickenpox. However, the virus remains in the body and can re-emerge to cause an attack of shingles, a condition that usually affects older people, which can cause an uncomfortable rash that is sometimes followed by prolonged pain (neuralgia) in the area of the rash.