The chickenpox rash initially appears as pinkish bumps a few millimetres across, usually on the chest or abdomen. Within hours the bumps develop into very itchy blisters, containing a clear fluid. These blisters are known as vesicles.
The vesicles break down quite rapidly and form crusts and scabs, but a new crop of vesicles appears just as the previous crop starts to crust.
Typically 250 to 500 vesicles will form during the chickenpox illness. The chickenpox rash is usually most clustered on the chest and abdomen, with fewer vesicles on the face and limbs.
Vesicles on the scalp may be accompanied by swollen lymph glands at the back of the neck. Along with the skin blisters, blisters may also occur in the mouth and throat, on the eyelids and in the genital and anal areas. In these areas the blisters tend to break down, forming painful ulcers.
Blisters in the mouth make eating or drinking difficult. The blisters usually stop forming by the fifth day of the rash, and most of these become crusted by sixth day of the illness.
While chickenpox is usually a mild illness in children, there are a number of possible complications, which are fortunately quite rare.
Chickenpox encephalitis may occur in about 1 in 1,000 cases, usually towards the end of the disease.
Chicken pox pneumonia is another possible complication, but it is less common in children than in adults.
What is chickenpox?
Risk factors for chickenpox
Revised and reviewed by Prof Eugene Weinberg, Paediatrician and Paediatric Allergist, Health24 expert, February 2015.