Incubation Period
(Duration: 7 to 17 days)
Not contagious

Exposure to the virus is followed by an incubation period during which people do not have any symptoms and may feel fine. This incubation period averages about 12 to 14 days but can range from 7 to 17 days. During this time, people are not contagious.

Initial Symptoms
(Duration: 2 to 4 days)
Sometimes contagious

Smallpox may be contagious when the initial symptoms are first exhibited, but is most infectious during the first 7 to 10 days following rash onset.

The first symptoms of smallpox include fever, malaise, head and body aches, and sometimes vomiting. The fever is usually high, in the range of 101 to 104 degrees Fahrenheit. At this time, people are usually too sick to carry on their normal activities. This phase may last for 2 to 4 days.

Early Rash
(Duration: about 4 days)
Most contagious

A rash emerges first as small red spots on the tongue and in the mouth. These spots develop into sores that break open and spread large amounts of the virus into the mouth and throat. At this time, the person becomes most contagious.

Around the time the sores in the mouth break down, a rash appears on the skin, starting on the face and spreading to the arms and legs and then to the hands and feet. Usually the rash spreads to all parts of the body within 24 hours. As the rash appears, the fever usually falls and the person may start to feel better.

By the third day of the rash, the rash becomes raised bumps. By the fourth day, the bumps fill with a thick, opaque fluid and often have a depression in the center that looks like a bellybutton. (This is a major distinguishing characteristic of smallpox.)

Fever often will rise again at this time and remain high until scabs form over the bumps.

Pustular rash
(Duration: about 5 days)
Contagious

The bumps become pustules – sharply raised, usually round and firm to the touch as if there is a small round object under the skin. People often say the bumps feel like BB pellets embedded in the skin.

Pustules and Scabs
(Duration: about 5 days)
Contagious

By the end of the second week after the rash appears, most of the sores have scabbed over.

Resolving Scabs
(Duration: about 6 days)
Contagious

The scabs begin to fall off, leaving marks on the skin that eventually become pitted scars. Most scabs will have fallen off three weeks after the rash appears. The person is contagious until all of the scabs have fallen off.

Scabs resolved
Not contagious

Scabs have fallen off. Person is no longer contagious.