Chickenpox is not the same as smallpox, it is two different infections. The causative agent of chickenpox is called varicella zoster virus, which is capable of causing chickenpox in the first infection and only causes shingles in the second infection. The chickenpox rash is centripetal, meaning that it is more on the trunk and less on the extremities. The chickenpox rash does not usually leave a scar after it has been removed because the lesions are shallow. Chickenpox is also usually not accompanied by particularly obvious complications, so many mild cases of chickenpox can be cured even without any treatment. Smallpox, on the other hand, is a more serious infection, and the rash of smallpox is usually centrifugally distributed, more on the head, face, hands, and feet than on the trunk. The smallpox rash is much more deeply damaged, so it leaves scars after it heals, and the scars are depressed and more frequent on the face, so you can grow a face of pockmarks after getting smallpox. Smallpox can also lead to more serious complications and has a significantly higher mortality rate than chickenpox.