The incubation period of chicken pox is long at 2 to 3 weeks. The child becomes pyrexial and feels generally unwell. Within hours the rash appears on the face, scalp, chest, back and abdomen.
The rash starts as a pink macule (spot) which soon becomes a papule (palpable) and then a vesicle (with clear fluid) which progresses to a pustule (containing pus) and finally a scab. The progression takes 1–2 days and the rash, which is very itchy, appears in crops for about 5 days. The rash also appears in the mouth as multiple small ulcers. Unless there is secondary infection (impetigo), the rash does not leave scars.
The diagnosis can almost always be made by finding the typical rash. Usually the illness is mild and is not complicated.
Rarely pneumonia or encephalitis may complicate chickenpox.