Chickenpox is an infectious disease caused by the varicella-zoster virus. It results in an itchy blister-like rash, tiredness and fever.

It appears first on the trunk and face, but can spread over the entire body. It may cause between 250 and 500 itchy blisters. The rash is no longer contagious when all of the spots are crusted over and no new spots are appearing. This usually takes 7 days from the start of the rash.