Chickenpox is an airborne disease spread easily through coughing or sneezing of ill individuals or through direct contact with secretions from the rash. A person with chickenpox is infectious one to two days before the rash appears. They remain contagious until all lesions have crusted over (this takes approximately six days). Immunocompromised patients are contagious during the entire period as new lesions keep appearing. Crusted lesions are not contagious.

It takes from 10 to 21 days after initial infection for the disease to develop.

The onset of illness with chickenpox is often characterized by symptoms including myalgia, itching, nausea, fever, headache, sore throat, pain in both ears, complaints of pressure in head or swollen face, and malaise in adolescents and adults. In children, the first symptom is usually the development of a papular rash, followed by development of malaise, fever (a body temperature of 38 °C (100 Â°F), but may be as high as 42 °C (108 Â°F) in rare cases), sometimes severe back pains to the lower back, and anorexia (loss of appetite, not to be confused with anorexia nervosa). Typically, the disease is more severe in adults. Chickenpox is rarely fatal, although it is generally more severe in adult males than in adult females or children. Non-immune pregnant women and those with a suppressed immune system are at highest risk of serious complications. Chickenpox is believed to be the cause of one third of stroke cases in children. The most common late complication of chickenpox is shingles, caused by reactivation of the varicella zoster virus decades after the initial episode of chickenpox.