Is anal oral sex dangerous no matter how much my girlfriend cleans?

Use Protection. The anal area has a lot of bacteria, and everyone has a different balance. There is no way to cleanse all of the bacteria out. You run the risk of sexually transmitted diseases such as HIV, hepatitis, gonorrhea, as well as GI infections. If you wish to be more safe (no such thing as completely safe), use a piece of plastic wrap or a dental dam (piece of latex sheeting) over the entire area.