Chickenpox is a viral disease characterized by itching and a skin rash with fluid-filled blisters that burst and form crusts. The onset of the chickenpox rash may be preceded by fever and general malaise.

The rash begins with a few small, reddish bumps (papules) that quickly fill with fluid to form small blisters (vesicles). The vesicles appear in "crops," small groupings, first on the trunk then spreading to the extremities, face, and scalp over a period of two to four days.

The rash may spread into the mouth and other internal parts of the body. The vesicles break, and a light brown scab or crust forms over the top. This crust gradually darkens to a dark brown before it finally falls off, usually within two weeks of the onset of the illness.

Chickenpox itself seldom causes scarring. However, chickenpox lesions can become infected, often due to vigorous scratching. Some of these secondary infections may be severe enough to require hospitalization.

Chickenpox is spread from person-to-person by contact with infected respiratory droplets, or by contact with articles freshly soiled by discharge from the lesions. It is contagious from two days before the onset of the rash, until all of the lesions are crusted over.

The incubation period is 10 to 21 days. There is universal susceptibility to the virus in those not vaccinated or previously infected. After infection, lifelong immunity against recurrent infection is usually present. However, a person with a history of chickenpox may develop shingles (herpes zoster) later in life.