A person with chickenpox is contagious one to two days before blisters appear, and he is contagious until crusts form over all the blisters, states MedlinePlus. The chickenpox virus spreads through the air and via direct contact with infected bodily fluids, including fluids from the blisters, says KidsHealth.
The chickenpox rash appears within 10 to 21 days of exposure to an infected person, explains MedlinePlus. Early chickenpox symptoms include fever, headache and stomach ache. Itchy, fluid-filled blisters then form on reddened skin on the face, scalp or middle of the body before spreading to cover the entire body. The blisters then form crusts and fall off. The chickenpox vaccine normally prevents the disease; vaccinated individuals who develop chickenpox experience a mild form of the disease.