When you really think about it

That's why you need to use baby wipes whenever possible!!!!

Your bum hole is conveniently placed up in between your bum cheeks and therefore is naturally designed not to be in contact with anything as long as you don't (a) wear a thong or (b) dig around scratching up there like you're prospecting for gold or something. It's a dark crevice that harbors bacteria (but not as much as your mouth!) and leaks a bit even after you've wiped with a prepackaged antibacterial surgical swipe. For thousands of years folks have been using all sorts of stuff to wipe their sphincters (straw in the medieval period, ouch!) and they're all dead now but not because of some stinky bum touchy disease (some maybe but leave my uncle Frank out of this). So what I'm saying is don't get anal about wiping every last molecule up (pun intended).