In the presence of small pox in a community its differentiation from
some cases of chicken pox is important but sometimes difficult. One
of the most striking differences between the two diseases is that in
chicken pox the lesions occur in crops, all the stages of the eruption
being present at the same time, while in small pox the lesions are
all the same sort at any time. Another difference consists in the
distribution of the eruption, in chicken pox most is on the covered
parts of the body while in small pox the eruption is most abundant on
the exposed parts of the skin, the face, wrists and hands. The presence
of a fairly recent vaccination scar is always strong evidence against
small pox.