Chickenpox (varicella) is an illness that causes an itchy rash and red spots or blisters all over the body. The blisters burst and crust over after several days. Chickenpox is very contagious. People who are infected with the virus can spread it before they have any symptoms.
Chickenpox usually isn't serious in children. It can be more serious in newborns, teenagers, adults, pregnant women, and people who have a weakened immune system.