Anal sex or anal intercourse is generally the insertion and thrusting of the erect penis into a person's anus , or anus and rectum , for sexual pleasure. While anal sex is commonly associated with male homosexuality , research shows that not all gay males engage in anal sex and that it is not uncommon in heterosexual relationships. As with most forms of sexual activity, anal sex participants risk contracting sexually transmitted infections STIs. 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 lubrication like the vagina does , so they can easily tear and permit disease transmission, especially if a personal lubricant is not used.