Since the lining of the anus is very thin and can tear easily, it is much easier for a person to be exposed to a sexually transmitted disease during anal sex. Also, when a penis is inserted into the anus and the penis ejaculates, the semen can drip into the vaginal opening if the partner is a girl. This can increase her risk of becoming pregnant.

For these reasons, it is very important to always use a lubricated latex or polyurethane condom for anal intercourse. A penis or object should never be inserted into the vagina or the mouth after it has been inside the anus, without washing the penis or object first. Rectal bacteria can be very harmful if it gets inside the vagina or inside the mouth.