Anal sex has been strongly tabooed in many Western countries since the Middle Ages, and is still illegal in some jurisdictions (see Sodomy law). Although practiced by many heterosexual couples, it has often been associated with homosexual men. Like persons of other sexual proclivities, some gay men enjoy sexual activities of this kind while many others do not.
Heterosexual couples have often used anal intercourse as a means of contraception/birth control. It should probably be considered a fairly reliable but not foolproof method, as is possible for semen to contact the vulva and result in pregnancy.
Anal sex is an effective means of transmitting most sexually transmitted diseases. In particular, it is the sexual activity which most effectively transmits the HIV (AIDS) virus. Health care professionals suggest that condoms should always be used for anal intercourse, but they should by no means be considered an absolute safeguard. The best suggestion is to avoid anal sex with anyone known to have a sexually transmissable disease, and indeed anyone whose disease-negative status you aren't certain of.
Anal sex does carry some risks to health and comfort even in the absence of a risk of sexually transmitted disease. The vagina is well adapted to sex, being strengthened for this activity and secreting its own lubrication, whereas the anus and rectum are not. Thus, artificial lubrication is generally used in anal sex (oil-based lubricants like Vaseline destroy latex condoms, and the two should not be used together). The anorectal muscles are largely under involuntary control, making slow, gentle, and responsive insertion necessary to avoid pain. Additionally, nothing which has been placed in the anus should ever contact the female vulva or vagina without being thoroughly washed with soap or a similar disinfectant, to avoid infection caused by the transmission of inappropriate bacteria to this area.