Disseminated herpes simplex, typically in an immunocompromised host, can mimic chickenpox but is confirmed by viral culture or PCR for HSV.
Bacterial folliculitis presents as monomorphic pustules centered on hair follicles and lacks the characteristic progression from macule to vesicle ("dewdrop on a rose petal") seen in chickenpox.
This viral illness is distinguished by its characteristic distribution of lesions on the hands, feet, and inside the mouth, whereas chickenpox has a centripetal (trunk-first) distribution.
Primary gingivostomatitis involves the mouth, while eczema herpeticum involves areas of eczema; neither has the widespread, scattered vesicular rash of chickenpox.
Shingles (herpes zoster) is a reactivation of the same virus but is distinguished by its strict unilateral, dermatomal distribution, unlike the diffuse spread of primary chickenpox.
Eradicated globally, smallpox was distinguished by its lesions being all in the same stage of development (synchronous) and having a centrifugal (limbs-first) distribution.