Chickenpox (varicella) is a contagious illness that causes an itchy rash and red spots or blisters (pox) all over the body. It takes about 1 or 2 days for a chickenpox red spot (macule) to go through all of its stages. This includes blistering, bursting, drying, and crusting over. New red spots appear every day for up to 5 to 7 days.