Chickenpox and Smallpox Rash Comparison

How initial symptoms differ

0 to 2 days of mild illness pass before the rash develops.

2 to 3 days of severe illness pass before the rash develops.

Lesions first appear on the face or trunk.

Lesions first appear in the throat or mouth, then on the face, or on the upper arms.

How the rash lesions differ

Lesions develop in successive fashion. While some are new, others are crusting over (in "crops").

Lesions develop at the same time, and they look alike on any one section of the body, such as the abdomen, arms, or face.

Lesions change rapidly, crusting over within 24 hours.

Lesions change slowly, scabbing over after 9 to 15 days.

Lesions sit on the skin surface and look like small blisters.

Lesions become firm, dome-shaped, and deep in the skin.

Rash rarely develops on palms and soles.

Rash commonly develops on palms of the hands and soles of the feet.

Lesions are most concentrated on the torso, with fewest on the hands and feet. Lesions can affect the face and scalp, but rarely affect the entire body equally.

Lesions are most concentrated on the face, hands, and feet.