What is smallpox?

Smallpox is a serious, contagious, and sometimes fatal infectious disease caused by a virus called the variola virus. The disease gets its name from the Latin word for “spotted” and refers to the small pus-filled blisters that appear on the face and body of an infected person.

The smallpox vaccine offers the best protection against contracting the smallpox virus.

Is smallpox fatal?

About 30% of people who become infected with smallpox die from their illness.

How is smallpox spread?

Smallpox is spread from person to person by several means, including:

  • Direct, face-to-face, and fairly prolonged contact with an infected person. For instance, the saliva of the infected person can spread the disease.
  • Direct contact with the fluid in the blisters in the infected person's skin or other infected bodily fluids
  • Direct contact with contaminated objects, such as blankets, towels or clothes touched by an infected person Smallpox is rarely spread through the air in settings such as buses, trains, or office buildings.

What are the symptoms of smallpox?

People infected with smallpox develop some symptoms (for example, fever, headache, backache, and general fatigue) that are typical of many less serious diseases. However, the telltale sign is the development of a unique skin rash. The rash, which has an indentation (hollow area) at its center, covers the entire body. The rash progresses to a raised bump, then to a pus-filled blister that crusts and scabs over before finally falling off about three weeks later, leaving behind a pitted scar.

How long does it take smallpox symptoms to appear?

After exposure, there's a period of seven to 17 days (called the incubation period) during which an infected person may not show any symptoms. Then, over the next two to four days, an infected person may become sick with cold and flu-like symptoms (this is called the prodromal stage). The classic smallpox rash begins after these cold and flu symptoms disappear. So, the earliest outward symptoms of smallpox would appear about nine days after exposure, when the rash develops.

A person with smallpox is most contagious to others while the rash is present, but is still considered contagious until the last smallpox scab falls off. A person is not contagious during the incubation period, and only sometimes contagious during the prodromal stage.


Last reviewed by a Cleveland Clinic medical professional on 01/17/2017.


  • Centers for Disease Control and Prevention. Smallpox Accessed 1/24/2017.
  • National Institute of Allergy and Infectious Diseases. Smallpox Accessed 1/24/2017.

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