I’m just curious why are assholes which is constantly exposed to germs is not causing any infections or at least getting irritation from being constantly exposed to shit which is dirty.
They’re being exposed to bacteria that are already present in your lower digestive tract. Those bacteria can be harmful *if you eat them* (fecal-oral is a very common way that food poisoning bacteria spread), but they’re not dangerous in your intestines or (directly) dangerous on your skin (except that having them on the skin of, say, your hands can be a good way to end up with them in your mouth).
First reason is that mucosal tissue creates a physical barrier that is very hard for microbes to get through. Additionally, the vast majority of lymphocytes in your body are found in those tissues. And your immune system is just in general much more active there too. When cells detect an invading organism they don’t call for help, they just initiate the immune response themselves.
Of course, it would be horrible for our entire bodies to be composed of this sort of tissue. its great against microbes, but not so great about mechanical damage. So you only find it where its most important.
So, our entire digestive system is technically the “outside” of out bodies. Our immune system keeps most little breaches that might happen under control. There also a healthy supply of “good” bacteria inside of us, that usually helps keep “bad” bacteria from taking hold.