Anal sex (also called anal intercourse) is the act in which the penis is inserted into the anus of a sexual partner. The term can also include other sexual acts involving the anus, including pegging, anilingus, fingering, and object insertion.
While anal sex is commonly associated with male homosexuality, research shows not all gay males engage in anal sex and that it is not uncommon in heterosexual relationships. Types of anal sex can also be a part of lesbian sexual practices.
Many people find anal sex pleasurable, and some may reach orgasm through anal penetration — by stimulation of the prostate in men, indirect clitoral/G-Spot stimulation in women, and associated sensory nerves (especially the pudendal nerve). However, many people find anal sex painful as well, sometimes extremely so, which may be primarily due to psychological factors in some cases.
As with most forms of sexual interaction, anal sex participants risk contracting sexually transmitted diseases; anal sex is considered a high-risk sexual practice because of the vulnerability of the anus and rectum. The anal and rectal tissues are delicate and do not provide natural lubrication, so they can easily tear and permit disease transmission, especially if lubricant is not used. Unprotected anal sex is considered the riskiest form of sexual intercourse, and therefore authorities such as the World Health Organization (WHO) issue recommendations for making anal sex safer.