Differences between chicken pox and small pox

Small pox Chicken pox
Incubation period
(approximately)
12 days 15 days
Prodromal symptoms Severe Mild
Rash – sites affected Extensor surfaces, palms, soles Flexor surfaces, axilla
Rash – features Deep seated Superficial
Single stage or rash present at a time Multiple stages of rash at the same time (pleomorphic)
Multilocular, umbilicated vesicles Unilocular vesicles, classically ‘dew drop on rose petal’
No inflammation around rash Zone of inflammation present around rash
Rash – evolution Slow, all stages are visible Fast evolution of rash
Scab formation by 10-14 days of disappearance of rash Scab formation by 4-7 days of disappearance of rash
Fever Fever subsides with development of rash,
may appear again with formation of pustules
(secondary rise of temperature)
Fever occurs with each crop of vesicles