Inspired by this webcomic.

I understand that going back in time has the potential to expose you to a number of diseases that you have no resistance to (e.g.: the Bubonic Plague, Polio, Smallpox, etc.), but clearly this effect depends pretty heavily on exactly how far you go back in time.

Starting in modern times:

If you go back in time 10 years, you don't have to worry about disease (any more than usual), because the diseases present are roughly the same as the time you left.

If you go back in time 100 years, there are a few diseases you might encounter that could be a problem, like the Spanish Influenza or Smallpox. Many diseases though, you would be vaccinated against, even if they aren't common nowadays, like Polio and Whooping Cough.

If you go back in time 1000 years, you have a whole number of diseases that are you are not inoculated against, like the Bubonic Plague, Leprosy, and Smallpox. Even if you ignore those, pretty much every disease present at that time would be different enough from what you have encountered that your immune system is going to have to fight off a lot of minor diseases. See this post for more information.

If you go back far enough in time, say to the Paleolithic era, you no longer have to worry, because diseases don't spread very rapidly in hunter-gatherer environments. Any really deadly diseases would just wipe out one tribe and spread no further, meaning that all the disease around back then would be relatively benign.

If you go back even further, at some point the early hominids will be biologically different enough from you that any diseases that they have won't be able to effectively spread to you.

But what about the time in-between, around the time of the first civilizations? More broadly, would a time traveler to the Bronze Age--when humans were first really collecting in urban environments--have to worry about ancient diseases?

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    $\begingroup$ I disagree. Your logic applies to human-only diseases but it completely ignores the threat from species-jumping diseases. Most of the really dangerous stuff is species-jumping. $\endgroup$ – Loren Pechtel Oct 9 '15 at 4:44
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    $\begingroup$ Another question: would the natives have to fear the diseases the time traveller unknowingly carries with them? $\endgroup$ – Crissov Oct 9 '15 at 12:32
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    $\begingroup$ Related question about managing illness time traveling $\endgroup$ – Green Oct 9 '15 at 14:18

I'm quite sure the traveller would have to worry, just because the Bronze Age people had antibodies that the traveller may not have. So a not-so-serious disease for our ancients can be very dangerous for the traveller. It has already happened (lots of Indios died for the european diseases after European discovered America).

You should also remember that viruses and bacterias change over time, so the person may have antibodies for those illnesses, but in a different version. That's one of the reasons why influenza vaccines have to be different every year.

So the time traveller would have to avoid situations that can put him in danger (crowds, not-well-cooked food, too close contacts and so on). And even so he could be not so safe.


A modern time traveler to the Bronze Age would need to worry about diseases but just knowing how diseases spread would go a long way towards keeping themselves safe.

Certainly, vaccines for as broad a range of diseases as possible would be beneficial though this time traveler would have a difficult time getting a smallpox vaccine aa there have been no new cases in over 30 years.

Carrying a broad spectrum antibiotic would probably be enough for the vast majority of diseases as those pathogens haven't yet become superbugs through interaction with antibiotics.

Just simple food safety and proper hygiene will go a long long way. Boiling water to kill pathogens. A mosquito net to keep away the bugs. This is all basic stuff so unless the time traveler is going specifically to an plague period, simple precautions should be enough.


Welcome Gwen Stacy ^^^^. Please don't leave spiderman!!

Now to your question. Although we have successfully eliminated the risk of several diseases from our environment, we don't get many diseases due to another reason too.


I don't know if a vaccine is available for bubonic plague or not, but vaccines for tuberculosis, cholera, smallpox etc are widely available and are administered to children in early ages. So no, the risk of infection would not be as high as you think. Your real concern should be about the other nasty diseases. Malaria. Dysentry. Malnutrition diseases (rickets and stuff). These would destroy you far before the other ones do.


A modern traveler, just traveling to another part of the world is often told "Don't drink the water".

Things like the Spanish Flu might have just been a particularly virulent flu bug that humans have now adjusted to (ie. if the same bug were present today, and it may be, it no longer hits humans harder than other flu strains). OR the Spanish Flu was an especially virulent strain that luckily, for humans, went dormant after killing millions. (ie. if the same bug were present today, it would cause similar or even greater loss of life).

If diseases encountered fall into the first group, you should be good. If any diseases encountered fall into the second group, virulent and viral, good luck.


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