Anal sex among heterosexuals has become more common in the United States. The NSSHB study found that 20% of men ages 25 to 49 and women ages 20 to 39 reported anal sex in the last year. The percentages of people who have had anal sex at least once in their lifetimes have doubled—40% of men ages 25 to 59 and women ages 20 to 39 (Herbenick et al., 2010a).

The anus has dense groups of nerve endings that can respond erotically. Individu­als and couples may use anal stimulation for arousal and variety. Manually stroking the outside of the anal opening, inserting one or more fingers into the anus, or licking the anus can be pleasurable for some people during masturbation or partner sex. Some women report orgasmic response from anal intercourse (Masters & Johnson, 1970), and heterosexual and homosexual men often experience orgasm from stimulation dur­ing penetration. For others, anal sex is unappealing, uncomfortable, or painful (Carter et al., 2010). In fact, one study found that almost half of young heterosexual women had to discontinue their first anal intercourse because of pain or discomfort. These findings

highlight the importance of information, education, and partner communication about anal intercourse (Stulhofer & Ajdukovic, 2011).

Because the anus contains delicate tissues, special care needs to be taken during anal stimulation. A nonirritating lubricant and gentle penetration are necessary to avoid discomfort or injury. It is helpful to use lubrication on both the anus and the penis or whatever object is being inserted. The partner inserting needs to go slowly and gently, keeping the penis or other object tilted to follow the direction of the colon (Morin, 1981). It is essential for sex toys or other objects used for anal stimulation to have a larger base than tip; otherwise an object can slip past the anal opening and become trapped by the anal sphincter, requiring a trip to the emergency room to remove the object.

Important health risks are associated with anal intercourse (McBride & Fortenberry,

2010) . Heterosexual couples should never have vaginal intercourse directly following anal intercourse, because bacteria in the anus can cause vaginal infections. Oral stimula­tion of the anus, known as analingus (or, in slang, "rimming"), is extremely risky; various intestinal infections, hepatitis, and sexually transmitted infections can be contracted or spread through oral-anal contact, even with precautions of thorough washing. Careful use of a dental dam helps prevent transmission of bacteria and viruses.

Anal intercourse is one of the riskiest of all sexual behaviors associated with trans­mission of HIV, particularly for the receptive partner because tissue in the anus is rela­tively fragile and can tear easily. For women the risk of contracting this virus through unprotected anal intercourse is greater than the risk of contraction through unprotected vaginal intercourse (Maynard et al., 2009). Heterosexual and gay male couples who wish to reduce their risk of transmitting or contracting this deadly virus should use a condom or refrain from anal intercourse. In Chapter 15 we more fully discuss precau­tions to avoid transmission of HIV •