Although anal sex is often thought of as a strictly homosexual activity, many heterosexual couples enjoy it too. Anal penetration can be pleasurable, but it can also be a source of physical discomfort. The muscle on the outside of the rectum, called the anal sphincter, ordinarily tightens if stimulated, which means that attempts at insertion of the penis, or even a finger, may be uncomfortable even if done slowly and gently. If penetration into the anus is forced, injury is possible. It is helpful to use a lubricant liberally and to relax and gradually dilate the sphincter by gentle manual stimulation before attempting penetration.
Some people clear the rectum with a small disposable enema before anal intercourse.
Some people have strong negative attitudes toward anal sex, whether it takes place between homosexual or heterosexual couples. They may think of it as being unclean, unnatural, perverted, disgusting, or simply unappealing. It is sometimes regarded as the ultimate in depravity and has regularly been condemned by religious and secular authorities. Historically, religious objections originate from the fact that a woman cannot possibly get pregnant through anal sex, as some religions only approved of sexual intercourse for the purpose of reproduction. Anal sex is subject to legal restrictions in some states, even between married couples.