Unsafe Sex

V2, N6, December 1992

Research Update

Unprotected anal sex, particularly receptive anal intercourse whether male-to-male or male-to-female, has consistently been identified as the sexual behavior that poses the greatest HIV transmission risk. Vaginal sex is believed to be the next highest risk, especially for the female partner. Other sexual behaviors that may pose an HIV-related risk include oral sex; anal activities such as "fisting" and "rimming;" rectal douches and enemas; sharing of anal insertable "sex toys;" and activities that involve urine or feces when blood is present in them.

This Research Update reviews sexual behaviors that have been studied for their HIV infection risk.

Anal Sex

Over the past several years, receptive anal intercourse, which is practiced by people of all sexual orientations, has been identified as the most effective sexual route of HIV transmission. Although research related to anal sex exists, it has been hampered by the social taboo surrounding the behavior.

The relationship between unprotected receptive anal sex and HIV infection has been widely publicized and surveys have found high levels of awareness of its risks, particularly in the gay community.

While many gay men have responded to this risk by ceasing to have anal sex or lowering risk by using condoms, surveys have found that others still engage in unprotected anal sex. A survey of 823 gay and bisexual men in Los Angeles found that 21% reported episodes of unprotected receptive anal intercourse with ejaculation during the previous 30 days (1). In a survey of Latino and Filipino gay and bisexual men in San Francisco, 34% of Filipino and 47% of Latino men reported having unprotected anal sex in the previous year despite knowing about the HIV transmission risk of the behavior (2).

While receptive anal intercourse poses the greatest sexual risk for HIV infection, insertive anal intercourse is also a high- risk sexual behavior (3). Because rectal tissue is susceptible to damage during anal intercourse, researchers believe that HIV- infected blood or secretions form the traumatized rectal tissue of the receptive partner through small abrasions on the penis.

Although anal sex has traditionally been considered uncommon among heterosexuals, a recent review estimated that at least 10% of heterosexuals in the United States regularly engage in anal sex (4). In various surveys, nearly 20% of heterosexual men and 40% of women have reported engaging in anal sex during their lives (5). Surveys of teenage women have found that more than one in five report having had anal sex. Several recent studies of heterosexuals have found higher rates of HIV infection among those who engage in unprotected anal sex (6).

A survey of lesbians who had engaged in sex with men found that less than 25% engaged in anal intercourse if their partner was heterosexual, but nearly half engaged in anal sex if their partner was a bisexual man (7).

Vaginal Sex

About 5% of all AIDS cases in the United States [as of December, 1992] have been attributed to transmission through unprotected heterosexual intercourse, and epidemiologists project that rate of infection among non-drug using heterosexuals will double over the next five years (8). According to a national survey of sexual behavior, heterosexuals appear more often than not to engage in sex without condoms (9).

Unprotected vaginal intercourse places both partners at risk. Risk of transmission is considered higher from the man to the woman than from the woman to the man. Researchers believe HIV passes more easily into the bloodstream through the walls of the vagina and rectum than into the shaft of the penis. While unprotected vaginal sex is a high-risk behavior, the risk of infection from vaginal sex is less than the risk of infection from anal sex. This is true partly because the vaginal walls, unlike the rectum, expand to allow for the entry of a penis, thereby leading to less trauma (6). The risk of vaginal trauma increases as intercourse becomes more vigorous or when performed without consent.

It is not only self-identified heterosexuals who engage in vaginal intercourse. Surveys have found that some men who identify as gay and some women who identify as lesbian also engage in vaginal intercourse. In one study, 72% of men who identified as gay had, at some time in their lives, engaged in sex with female partners (10%). A national survey of lesbians found that nearly half had engaged in sex with men, both heterosexual and bisexual, in the previous 10 years.

Oral Sex

Oral sex is referred to as fellatio when performed from mouth to penis and as cunnilingus when performed from mouth to vulva. Studies have shown that most gays, lesbians and heterosexuals make oral sex a regular part of their sexual behavior. Fellatio is believed to be the most widely preferred form of sex among gay men (5). And, a survey found that nearly three quarters of those in heterosexual marriages have engaged in oral sex with their partners. Among young people, oral sex has occurred with increasing frequency and, in recent years, at younger ages. Among lesbians, a survey from 1983, the most recent study available, reported that 39% of lesbians usually or always engaged in cunnilingus during sex (5).

Researchers have found it difficult to isolate oral sex for study as a risk behavior for HIV because sexual activity usually involves other behaviors that are considered more likely to transmit HIV. However, several reports over the past two years have confirmed cases in which infection has occurred with unprotected male-to-male oral sex as the only known risk behavior (11).

Several factors increase the risk of infection during unprotected oral sex:

  • Poor oral hygiene or bleeding after tooth brushing;
  • Allergies or inflammation in the mouth or nasal cavities that may result in breaks in mucous membranes (12);
  • Use of alcohol and other drugs such as "crack," which may lead to particularly long oral sex sessions that may cause abrasions in the mouth (13): and
  • More physical and penetrative oral sex, which can occur with greater frequency as people replace other forms of unsafe sex with oral sex.


Rimming is oral contact with the anus and rectum. It often precedes anal intercourse and is correlated with other anal sex behaviors. One study of gay and bisexual men found that about 20% had rimmed their partners (10).

One study reported a relationship between rimming, oral contact with a partner's feces and the development of Kaposi's sarcoma (KS) among gay and bisexual men infected with HIV (14). KS, which is an AIDS-defining disease, developed in 75% of those with HIV who rimmed weekly compared to 18% of those who had never engaged in rimming. While the relationship between rimming and KS has been disputed, rimming has been strongly associated with the development of other sexually transmitted diseases (STDs), including hepatitis B and parasites.


Fisting, also known as hand-balling, refers to inserting the arm or at least three fingers into the anus or vagina. In studies of sexually active gay men, higher rates of HIV infection have occurred among those who engaged in receptive fisting compared to those who had not engaged in this activity (3,16). This higher rate is believed to be due to expansion or stretching of the anus and sphincter, which can cause injuries, including tears and bleeding. These injuries can allow HIV to enter the blood during fisting through cuts on the hand or, more likely, during unprotected anal sex, which often follows fisting (4).

In a study of gay and bisexual men, HIV infection rates were slightly higher among those who fisted without using protective gloves compared to those who used gloves. Those infected with HIV were more likely than those who were not infected to have engaged in fisting, although there was no evidence that this behavior was directly related to HIV infection (10). Studies have found rates of fisting between 2% and 12% among gay men (10,15). Heterosexual fisting has not been studied.

Enemas, Rectal Douches and Anal Insertables

Use of enemas, rectal douches and other anal insertable devices poses a risk for HIV infection. Enemas and rectal douches are sometimes given to cleanse the bowel before anal intercourse or fisting. These behaviors are considered by some to be erotic unto themselves. In one study, more than half the men infected with HIV, and more than one-quarter of those not infected, had douched before receptive anal intercourse. Enemas may cause perforation and inflammation, which allows entry of HIV-infected semen. Rectal mucosa can also be injured when insertable objects such as "anal plugs" and dildos are used (15).


Kissing is not considered a risk behavior for HIV, and there have been no reported cases of HIV transmission during kissing. It is believed to pose a possible risk for HIV if tissue of the mouth is broken and blood is present in saliva. A study of 45 heterosexual couples found blood present in the saliva of half the group (17). It was present in higher levels after tooth brushing and passionate kissing, which was defined as kissing that lasts several minutes with vigorous rubbing of the inside of the mouth.

Other Behaviors

"Watersports" refers to activities that involve urinating on the skin or into the mouth, and "scat" is defecating on someone or playing with or eating feces during sex. It is believed that HIV may be present in urine or feces only when blood is present in them. Even in the absence of blood, feces can transmit STDs and parasites.

Researches believe relatively few heterosexuals or homosexuals engage in behaviors involving urine or feces. Surveys have generally found that fewer than 2% of all people engage in activities involving direct contact with feces (10).


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