Everyone gets poop on their hands at some point. You wash your hands. Cool, all good.

....but at a point in time, soap handn't been invented yet. So when that happened, that's it, you just had those germs on you forever.

This is pretty high on my list of reasons why there's a limit on how far back I'd be willing to time travel.

I'm not sure it's normal to have given it so much thought.