Chickenpox (varicella) is a common contagious illness caused by a type of herpes virus. Chickenpox is most contagious from 2 to 3 days before a rash develops until blisters have crusted over.

Chickenpox is most common in children and is usually not serious. In teenagers, adults, pregnant women, and people who have impaired immune systems, chickenpox can be more serious.

The incubation period—the time from exposure to the chickenpox virus until a person develops symptoms—is usually 14 to 16 days but can be from 10 to 21 days. Symptoms of chickenpox include a fever, feeling ill, and the development of a widely scattered, itching rash with fluid-filled blisters. The blisters burst and crust over after several days. New blisters continue to develop for up to a week. A person infected with chickenpox can spread the virus before developing any symptoms.

Treatment for chickenpox focuses on preventing the person from scratching the rash and on relieving fever and discomfort. A vaccine to prevent chickenpox is available and recommended for children and for teens and adults who have not had chickenpox.