anal sex is when an erect penis or other device made for sexual pleasure is inserted into a sexual partner's anus. anal sex with a female does not lead to pregnancy by itself, however, semen can leak out of the anus and enter into the vagina, and pregnancy may rarely occur. anal sex can still pass sexually transmitted diseases from one partner to another. it can also be very unhealthy for the body because the skin around the anus can tear, bleed and get infected with bacteria. for safety and pleasure, partners often use condoms, female condoms and/or lubrication.