Chickenpox is contagious one to two days before the appearance of the rash until the blisters have dried and become scabs. Once infected, chickenpox may take up to 10 to 21 days to develop. Diagnosis usually involves a medical examination. Sometimes a secondary case of chickenpox does occur. Blood tests can confirm immunity to chickenpox in people who are unsure if they have had the disease.
Complications can occur from chickenpox.
Those most susceptible to severe cases of chickenpox are infants, adults, pregnant women, and people with impaired immune systems. Children with varicella should not be given aspirin because administration of salicylates to children with varicella increases the risk of Reye's syndrome.