Is anal sex safe?

Not really: Just like in any big city, some streets are one-way and some streets are two-way. A vagina is created or evolved to be a two-way street (penis in and out; baby out). However, the gastrointestinal tract is designed to be one-way, with an opening on each end. Food goes in the mouth, and the brown stuff goes out the butt. The exception is when one vomits what the body thinks is bad for the stomach.

Only if it's safe: Any kind of sex comes with risk unless proper precautions are taken. Anal sex will not cause pregnancy, of course, but is a higher-risk way to transit sexual infections if unprotected. Condoms prevent this spread, and use of a water-based lubricant with the condom will help prevent condom breakage (often happens with anal sex). Lubricant is also important to reduce cuts and trauma to the anus.