system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When someone has hemorrhoids, what keeps fecal matter from entering the bloodstream, potentially causing infection?
gpt
For the most part, your fecal matter isn't particularly dangerous to you.  Yes, you generally don't want the stuff that's in there to go anywhere but the toilet, but the real fear behind fecal contamination is that OTHER people's poop is very bad for you.  Additionally, poop is very attractive to bacteria and is a great host for growth.  Just like if you leave cooked food out, poop will grow bacteria that is all around us and make it get to unhealthy levels.

This in addition to other factors like positive pressure, and the simple fact that it DOES enter the bloodstream sometimes, but your body is constantly fighting off bacteria that you may not even realize.