The contagious period for chickenpox begins about one to two days before the itchy rash appears, lasting until the rash lesions crust, according to the Centers for Disease Control and Prevention. Approximately 90 percent of susceptible individuals become infected after close contact with someone who has the disease.
When someone infected with the chickenpox virus sneezes or coughs, the virus clinically known as varicella becomes airborne and spreads easily, notes the Centers for Disease Control and Prevention. Individuals also contract the highly contagious virus when they inhale or touch virus particles in the air that the chickenpox lesions produce. People typically develop chicken pox from 10 to 21 days after being exposed to the virus. Adults may experience fever before the rash begins, while children experience the rash without earlier symptoms.