After exposure to smallpox, how long does it take to show symptoms?
A. Following exposure, it takes between 7 and 17 days for symptoms of smallpox to appear (average incubation time is 12 days). During this time, the infected person is not contagious but becomes so with the onset of a rash. The characteristic rash follows in 2 to 3 days, with flat, red sores that evolve at the same rate and are most prominent on the face, arms and legs. People are most infectious during the time when the rash first develops, because that is when the largest amount of virus is present in the saliva. The sores become pus-filled after a few days and begin to crust early in the second week. Scabs develop and then separate, falling off after about 3 to 4 weeks, possibly leaving pitted scars.
