Chickenpox is a very contagious disease caused by the varicella-zoster virus. The virus spreads easily from people with chickenpox to others who have never had the disease or received the chickenpox vaccine. The virus spreads in the air when an infected person coughs or sneezes. It can also be spread by touching or breathing in the virus particles that come from chickenpox blisters.
Chickenpox can also be spread from people with shingles. Varicella-zoster virus also causes shingles. A person with shingles can spread the virus to others who have never had chickenpox or received the chickenpox vaccine. In these cases, the exposed person might develop chickenpox. For more information about how shingles spreads, see Transmission.