So basically op, it can be a number of things, like a history of stomach issues, straining too hard, constipation, sitting a lot, or even wiping too hard/too much. I had no idea about this either and ended up with the same problem, thanks to low quality tp at work scratching my ass. I got hems and had the issue ever since. I don't know about the prostate thing. But if you keep doing what you're doing, you'll make it worse. Try a new diet, kegal exercises, and tighten your ass when you wipe. This is also one thing bidets help prevent. You're right, it's not like anyone teaches you about these things, at least not until it's too late