Humans have been practicing anal sex since the beginning of time.
There's a certain amount of risk associated with anything a human does. If you're unlucky and/or stupid, you could kill yourself having anal sex.
But you could do the same blow-drying your hair or driving down the road.
If I were you, I'd learn the hazards and risks of anal sex in my native language and not try to figure out potentially life-threatening medical conditions in an anonymous online forum.
Penetration of the anus can be dangerous if it is performed haphazardly. If time is not taken to prepare for insertion ie lube, fingering etc the sphincter can quite easily be damaged. The sphincter is most commonly used for pushing Faeces from the body. It is not usually accustomed to being entered by an 8inch long 6inch think penis. Penetration is "abnormal" sphincter purely because it is not used to it. Anal sex is to some people more exciting that vaginal sex. All i can say from personal experience. Go slow and use lots of lube then reap the rewards.