The common name for the contagious illness medically known as varicella is chickenpox.
Chickenpox is caused by the varicella-zoster virus, a member of the herpesvirus family. It usually produces an itchy rash of small fluid-filled blisters, often accompanied by fever, tiredness and headache. The rash commonly begins on the chest, back or face before spreading elsewhere, and the illness is generally more severe in adults than in children.
The virus spreads easily through the air and through contact with blister fluid. An infected person can be contagious one to two days before the rash appears and remains so until the lesions crust over. Symptoms often begin 10 to 21 days after exposure. Vaccination substantially reduces the risk of infection and serious complications.
Chickenpox and shingles are related but not identical. After chickenpox, the virus can remain dormant in nerve tissue and later reactivate as shingles. Someone with shingles can transmit the virus to a non-immune person, causing chickenpox rather than shingles.