Chickenpox And Smallpox: What Are The Differences?

If you want to learn more about chickenpox and smallpox and what makes the two diseases so different, you’ve come to the right place!

Chickenpox And Smallpox: What Are The Differences?

While chickenpox and smallpox might both seem quite similar, causing blisters and rashes and both containing “pox” in their names, the two diseases are actually both completely different from one another. 

For starters, no cases of smallpox have been identified in the United States for over 65 years. On the other hand, new cases of chickenpox are treated every day.

Today, we want to share with you the main difference between chickenpox and smallpox.

We’ll take you through a number of key factors including the symptoms of both diseases, how severe they can be, and the average incubation period. 

This should help you easily understand the differences between the two, so let’s dive straight in!

What Is Chickenpox?

Chickenpox is a highly contagious infection caused by a virus called the varicella-zoster virus.

Extremely common in children and spread through direct contact, whether it be touch, coughing, or sneezing, chickenpox causes itchy spots on the skin, rashes, blisters, and pain in the mouth. 

It is fairly mild when compared to other diseases and tends to fade away after 1 to 2 weeks. 

What Is Smallpox?

Caused by the variola virus, smallpox is an acute contagious disease that once devastated the world.

Known as one of the most devastating diseases to ever hit humanity, leading to millions of deaths, symptoms include skin rashes, a fever, scarring, blindness, and toximemia.

Toximemia as well as system shock is what caused most deaths. It is believed smallpox existed for 3,000 years. 

What Are The Main Differences Between Chickenpox And Smallpox?

Now you know what each disease is, we can start looking in more detail at how they are both different.

While it is clear to see that chickenpox is a lot milder than smallpox and nowhere near as deadly, there is still a lot to learn.

To show you how the two diseases are different, we’ll now take you through some of the most important points.


Talking about severity seems like a reasonable place to start, seeing as though one of the two diseases is one of the worst diseases to hit humanity. 

When it comes to chickenpox, there’s not too much to worry about. Most cases are very mild and quickly leave the body.

Having said that, the disease can be quite serious if it causes any bacterial infections.

However, chickenpox is nowhere near as severe as smallpox. Smallpox is responsible for killing over 300 million people.

Even when individuals survived the disease they were often left with serious scarring and blindness. 

Initial Symptoms

While the symptoms of both diseases can be quite similar, initial symptoms tend to last for different lengths of time and be more or less severe.

For example, individuals who catch chickenpox can expect to experience mild illness for zero to two days, with a rash to follow.

Those who catch smallpox would likely experience severe illness for two to three days with a rash to follow.

Chickenpox And Smallpox: What Are The Differences?

Incubation Period

Both diseases also have different incubation periods. Smallpox has a shorter incubation period than chickenpox.

While chickenpox has an incubation period of 14-21 days, smallpox has an incubation period of 7 to 17 days. 

Causative Agent

Despite both diseases producing similar symptoms, they are both caused by different viruses. Chickenpox is caused by a virus called the varicella-zoster virus, also known as the herpes virus.

On the other hand, smallpox is caused by the variola virus, commonly referred to as the pox virus.


When it comes to prevalence, chickenpox is the disease out of the two that is still prevalent today.

This may surprise you because of how deadly smallpox is, but when you consider how desperately the disease had to be stopped, it makes perfect sense.

Luckily for humanity, smallpox has been completely eradicated from the planet. In fact, the last known case of smallpox was reported in Russia in 1978. It was the first disease to ever be eradicated.

On the other hand, chickenpox, up until recently, affected 4 million people every year. The new chickenpox vaccine is reducing this figure though.

Rash Lesions

There are also a number of key differences to note between the rashes both diseases cause. 

Lesions caused by chickenpox develop successively, leaving new and old lesions on the body. They normally crust over in just 24 hours and very rarely develop on the palms and soles.

It is uncommon for any illness to follow the chickenpox rash.

Smallpox on the other hand causes rashes that form at the same time anywhere on the body. They will then change slowly over time, typically taking from 9 to 15 days to scab over.

Unlike chickenpox, fever, vomiting, malaise, headaches, and rigors all follow the smallpox rash after two or three days.


The scabs caused by both diseases also act quite differently. The scabs caused by smallpox can be infectious, forming after 10 to 14 days. These scabs might only then fall off after 28 days.

Scabs caused by chickenpox start to form after four or five days and aren’t infectious. They will also start to fall off within 14 days.


A fever caused by chickenpox will only occur with each crop of vesicles. Fevers caused by smallpox subside with the development of any rashes.

They may then reappear with the formation of pustules.

Final Thoughts

Hopefully, now you’ve read this post, you should have a much better understanding of what makes chickenpox and smallpox so different. 

While both diseases might seem the same in terms of symptoms, from the information we have provided you can see how wildly different they are. 

Jennifer Dawkins

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