I have had some bleeding and some tears of the entrance to the anus which resulted in bleeding--nothing too serious. The key is lots of lube. I have never been seriously injured by a penis. Most of my tearing and bleeding was caused by dildos and foreign objects (one night a guy pushed a large flashlight in me, and I bled for several days. Never saw the doctor, which is probably stupid.) Prolapses can come from being fisted, but I have never had that happen, but I don't take huge fists.