What type of rash indicates exposure to smallpox rather than chickenpox?

A centrifugal rash pattern is indicative of smallpox, distinguishing it from chickenpox. In smallpox, the rash typically begins on the face and extremities and then spreads to the trunk, which exemplifies the centrifugal pattern. The lesions progress simultaneously across the body, and by the end of the rash evolution, they present as firm, raised pustules.

In contrast, chickenpox tends to exhibit a centripetal rash pattern, where the lesions primarily appear on the trunk and face with relatively fewer lesions on the limbs. Additionally, chickenpox features lesions that progress at varying rates, resulting in different stages of lesions being present simultaneously.

Understanding the differences in the rash patterns is crucial for differentiating between these two diseases, especially in clinical settings where prompt recognition can influence treatment and infection control measures.