The risk of getting HIV varies widely depending on the type of sexual activity. Anal sex (intercourse), which involves inserting the penis into the anus, carries the highest risk of transmitting HIV if either partner is HIV-positive. You can lower your risk for getting and transmitting HIV by using condoms correctly and consistently, choosing lower risk sexual activities, taking daily medicine to prevent HIV, called pre-exposure prophylaxis (PrEP); and taking medicines to treat HIV if living with HIV, called antiretroviral therapy (ART). Using more than one of these options at the same time provides even greater protection.
is the highest-risk sexual behavior for HIV transmission. Vaginal sex has a lower risk, and activities like oral sex, touching, and kissing carry little to no risk for getting or transmitting HIV. The vast majority of men who get HIV get it through anal sex. However, anal sex is also one of the ways women can get HIV.
The risk of human immunodeficiency virus (HIV) through unprotected anal intercourse is seen to be extremely high, as much 18 times greater than vaginal intercourse.
The reasons for the increased risk are well known and include such factors as:
- The fragility of rectal tissues, which allow the virus direct access into the bloodstream through tiny tears or abrasions
- The porousness of rectal tissues, providing access even when undamaged
- The high concentration of HIV in semen and pre-seminal fluid, which doubles the risk of infection with every one-log (one digit) rise in the person’s viral load (the amount of virus able to be detected in a person who’s infected)
- Furthermore, the secretion of blood from damaged rectal tissues can increase the risk for the insertive (“top”) partner, providing the virus a route of transmission through the urethra and tissues that line the head of the penis (particularly under the foreskin).
Risks to insertive and receptive partners
There is a widespread belief among gay men that the insertive partner (‘top’) is at very low risk of HIV infection. It is true that HIV infection occurs less frequently in men who solely take the insertive role than in men who engage in both roles, or men who practise receptive anal intercourse only (Jin).
However, being the insertive partner in condomless sex remains a high-risk activity. The per-act risk for the insertive partner in anal sex is comparable to the per-act risk for the male (insertive) partner in vaginal sex.
The receptive partner (‘bottom’) is at risk of infection from HIV in the semen and pre-seminal fluids (‘pre-cum’) of the infected partner. Rectal tissue is delicate and easily damaged, which can give the virus direct access to the bloodstream. However, such tissue damage is not necessary for infection to occur: the rectal tissue itself is rich in cells which are directly susceptible to infection.
The insertive partner (‘top’) is also at risk of infection, as there are high levels of HIV in rectal secretions, as well as blood from the rectal tissues (Zuckerman). This creates a risk of transmission to the insertive partner through the tissue in the urethra and on the head of the penis – particularly underneath the foreskin.
Several systematic reviews of studies have calculated that condomless receptive anal intercourse posed approximately ten to twelve times greater risk of infection than insertive anal intercourse.
The most recent review of the evidence estimated that for each condomless act with an HIV-positive partner, the risk of infection was 1.38% (one in 72 chance) for the receptive partner and 0.11% (one in 909 chance) for the insertive partner (Patel).
Nonetheless, many of the studies were carried out before antiretroviral treatment after diagnosis became the norm and so are likely to over-estimate the risk of infection.
Anal intercourse between men and women
Anal intercourse between men and women has generally not received as much attention as anal intercourse between men. However, there is evidence that anal sex is practiced by large numbers of sexually active adults. In 2010, 11% of women and 13% of men in the United Kingdom report having anal intercourse in the past year, with younger generations being more likely to report it (Mercer).
Unprotected heterosexual anal sex probably plays an important role in HIV transmission among heterosexuals, although reliable estimates are lacking (Baggaley).
Poppers are nitrite-based inhalants, widely used as a recreational drug by gay men in many countries. Especially popular for use during receptive anal intercourse, sniffing poppers relaxes the anal sphincter muscles, making intercourse easier and intensifying pleasure.
However, using poppers during unprotected, receptive anal intercourse more than doubles the risk of HIV infection (Macdonald). This may be because poppers increase blood flow to the rectal tissues, heightening their susceptibility to infection. Poppers do not affect the insertive partner’s risk of infection.
Rectal douching is the insertion of a liquid, such as tap water or soapsuds, into the rectum via a tool, to cleanse the rectum before or after anal sex and is a common activity among gay and bisexual men. However, it may damage the rectal lining and remove protective naturally occurring bacteria. If the same douching bulb, showerhead or other tool is used by different people, infections could also be transmitted that way.
A synthesis of 24 studies showed that rectal douching was associated with an almost threefold increased odds of infection with HIV and a more than twofold increase in the risk of a sexually transmitted infection other than HIV (Li).
While it is possible that this result could simply be due to behavioural differences, most of the studies performed multiple analyses to take into account potential confounders such as frequency of sex and partner numbers.
Rectal bleeding also raises the risk of infection, and could be caused by haemorrhoids, certain STIs such as anal warts, herpes lesions, the prior use of sex toys, or by fingering and fisting.
There are some data from low and middle-income countries to suggest that circumcision may be protective, but only for men who exclusively take the insertive role (Yuan).
Risk of HIV
Anal sex is the highest-risk sexual behavior for HIV transmission. Vaginal sex has a lower risk, and activities like oral sex, touching, and kissing carry little to no risk for getting or transmitting HIV. The vast majority of men who get HIV get it through anal sex. However, anal sex is also one of the ways women can get HIV.
Receptive Versus Insertive Sex
During anal sex, the partner inserting the penis is called the insertive partner (or top), and the partner receiving the penis is called the receptive partner (or bottom).
Receptive anal sex
is much riskier for getting HIV. The bottom partner is 13 times more likely to get infected than the top. However, it’s possible for either partner to get HIV through anal sex.
Being a receptive partner during anal sex
is the highest-risk sexual activity for getting HIV. The bottom’s risk of getting HIV is very high because the lining of the rectum is thin and may allow HIV to enter the body during anal sex from body fluids that carry HIV, including blood, semen (cum), pre-seminal fluid (pre-cum), or rectal fluids of a person who has HIV. Using condoms or medicines to protect against transmission can decrease this risk.
The insertive partner is also at risk for getting HIV during anal sex. HIV may enter the top partner’s body through the opening at the tip of the penis (or urethra) or through small cuts, scratches, or open sores on the penis. Using condoms or medicines to protect against transmission can decrease this risk.
Risk of Other Infections
In addition to HIV, a person can get other sexually transmitted diseases (STDs) like chlamydia and gonorrhea from anal sex without condoms. Even if a condom is used, some STDs can still be transmitted through skin-to-skin contact (like syphilis or herpes). One can also get hepatitis A, B, and C; parasites like Giardia and intestinal amoebas; and bacteria like Shigella, Salmonella, Campylobacter, and E. coli from anal sex without a condom because they’re transmitted through feces. Getting tested and treated for STDs reduces a person’s chances of getting or transmitting HIV through anal sex. If one has never had hepatitis A or B, there are vaccines to prevent them. A health care provider can make recommendations about vaccines.
Reducing the Risk
Condoms and Lubrication
Latex or polyurethane male condoms are highly effective in preventing HIV and certain other STDs when used correctly from start to finish for each act of anal sex. People who report using condoms consistently reduced their risk of getting HIV through insertive anal sex with an HIV-positive partner, on average, by 63%, and receptive anal sex with an HIV-positive partner, on average, by 72%. Condoms are much less effective when not used consistently. It is also important that sufficient water- or silicone-based lubricant be used during anal sex to prevent condom breakage and tearing of tissue. Female nitrile condoms can also prevent HIV and some other STDs. Since condoms are not 100% effective, consider using other prevention methods to further reduce your risk.
People who are HIV-negative and at very high risk for HIV can take daily medicine to prevent HIV. Pre-exposure prophylaxis (PrEP), if taken consistently, can reduce the risk of getting HIV from sex by more than 90%. PrEP is much less effective when it is not taken consistently. Since PrEP is not 100% effective at preventing HIV, consider using other prevention methods to further reduce your risk. Only condoms can help protect against other STDs.
Post-exposure prophylaxis (PEP) means taking antiretroviral medicines — medicines used to treat HIV — after being potentially exposed to HIV during sex to prevent becoming infected. PEP should be used only in emergency situations and must be started within 72 hours after a possible exposure to HIV, but the sooner the better. PEP must be taken once or twice daily for 28 days. When administered correctly, PEP is effective in preventing HIV, but not 100%. To obtain PEP, contact your health care provider, your local or state health department, or go to an emergency room.
For those living with HIV, antiretroviral therapy (ART) can reduce the amount of virus in the blood and body fluids to very low levels, if taken the right way, every day. When taken consistently, ART can reduce the risk of HIV transmission to a negative partner by 96%. Since ART is not 100% effective at preventing HIV, consider using other prevention methods to further reduce your risk. Only condoms can help protect against some other STDs.
Other Ways to Reduce the Risk
People who engage in anal sex can make other behavioral choices to lower their risk of getting or transmitting HIV. These individuals can:
- Choose less risky behaviors like oral sex, which has little to no risk of transmission.
- Get tested and treated for other STDs.
What Is the Risk of HIV From Anal Sex?
Anal Sex and HIV Risk
Anal sex and the risk of HIV transmission