Anal Cancer
Chlamydia trachomatis
Cryptosporidium
Giardia lamblia
Herpes simplex virus
Human immunodeficiency virus
Human papilloma virus
Isospora belli
Microsporidia
Gonorrhea
Viral hepatitis types B & C
Syphilis25
Kay, I gotta call Bad Science. For the record, almost none of this is a danger of having anal sex. You don't get syphilis from doing anal; you get it from doing an infected partner. Yes, odds of transmission vary for types of entry, but if you're relying on less tearing to stay safe you're pretty much fucked, anyhow. Same goes for clamydia, gonorhea, hepititus, HIV, papilloma and giardia, and probably most of the rest up there; and tying cancer to physical trauma seems chancey at best. This list is more a commentary on subcultures than on anal hazards -- free sex is bad health.