The difference between smallpox and chickenpox is the different infected viruses, different symptoms and different prognosis. 1. Different infected viruses: smallpox and chickenpox are two different diseases, smallpox is mainly caused by smallpox virus infection, chickenpox is caused by varicella-zoster virus. 2. Symptoms are different: smallpox begins with symptoms such as high fever, chills, headache, back pain, joint pain, fatigue, etc., and then maculopapular rash will appear, which begins to occur in the mouth, face and arms, and then spreads rapidly to the trunk and legs, the maculopapular rash will turn into blisters about three days, and develops into pustules in the seventh day or so. Chickenpox usually has a fever for one to two days, then a red maculopapular rash appears, which turns into fluid-filled herpes after a few hours. 3. Prognosis is different: the mortality rate of smallpox is close to 30%, if it is smallpox mortality rate of 1%, if it is hemorrhagic smallpox mortality rate is as high as 97%. Chickenpox most of the prognosis is good very few patients with severe disease may be death. Smallpox and chickenpox are more serious infectious diseases, if you can not distinguish between them, you should consult a doctor in time to distinguish between them, and timely treatment.