The incubation period-the time from exposure to the chickenpox virus until you develop symptoms-is usually 14 to 16 days but can be from 10 to 21 days. The first symptoms of chickenpox infection include:

• A fever of 100.4F to 103F.
• Feeling sick, tired, and sluggish.
• Little or no appetite.
• Headache and sore throat.

The first symptoms are usually mild in children, but they can be severe in teens and adults. These symptoms may continue throughout the illness.

About 1 or 2 days after the first symptoms of chickenpox appear, an itchy rash develops. During a typical course of chickenpox:

• Red or swollen spots or bumps appear and turn into pimplelike blisters filled with clear or cloudy fluid.
• The blisters break open, often leaking fluid.
• A dry crust forms over the broken blisters as they heal.

Chickenpox is most contagious from 2 to 3 days before the rash develops until all the blisters have crusted over.

Other conditions may cause a similar rash.