The Risks of HIV from Unprotected Sex

Simple Facts That Can Help You Assess Risk, Prevent Infection

Couple in bed
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Sexual transmission is the primary mode of infection in almost all countries. There still remains a lot of uncertainty as to what the risk of transmission are and the ways one can protect oneself (or others) for acquiring HIV.

Follows is a list  of frequently asked questions that provide an overview of the specific risks and prevention methods available today:

What Is the highest risk sexual activity?

By far, anal sex is the highest-risk sexual practice, accounting for the high rates of infection seen in men who have sex with men (MSM).

Receptive anal sex "(bottoming") is far riskier than insertive anal sex because the mucous lining of the rectum is thin and porous, allowing HIV to penetrate vulnerable cells and tissues semen, pre-seminal fluid ("pre-cum") and blood. The insertive partner is also at risk  as HIV can enter through the penile opening (urethra) or through open cuts or sores on the penis.

Statistically speaking, condomless anal sex is seen to be as much as 18 times riskier than condomless vaginal sex.

How is HIV Spread Through Vaginal Sex?

In women, HIV can enter through the vulnerable tissues and cells of vagina and cervix, as well directly thrugh the cervix itself. Cuts or tears in her vagina only add to the vulnerability, as do sexually transmitted infections that can further compromise mucosal cells and the protective flora of the vagina. 

The route of transmission in men is essentially the same as with the insertive partner in anal sex.

The lack of circumcision can also add to a man's vulnerability. Research has shown that the high level of bacterial activity beneath the foreskin of an uncircumcised penis can, in fact, potentiate HIV infection. The activation of an immune response triggered by the bacterial population often results in the availability of CD4 T-cells to the region—the very cells that HIV targets for infection.

Can You Get HIV From Oral Sex?

The risk of HIV from oral sex is generally considered to be small to minimal. The riskiest oral sex practice is fellatio ("blowjob") with ejaculation into the mouth. Having cuts, sores or a sexually transmitted infection can also increase a person's risk.

Oral-anal ("rimming") and oral-vaginal sex("cunnilingus") are considered to be of almost negligible risk, although the former can result in any number of bacterial, protozoal or viral infections.

Can HIV be Transmitted Between Two Women?

Sex between women who have sex with women (WSW) is a rare, although incidences have occurred. Generally speaking, such instances have been typified by a partner with a high HIV viral load, "rough sex" that has compromised vaginal tissues, and the use of shared sex toys.

What Can I Do To Protect Myself?

While condoms remain the first-line defense is preventing the spread of HIV, the daily use of HIV pre-exposure prophylaxis (PrEP) has also been shown to have high efficacy in prevention between two people.

Consisting of a daily oral tablet, PrEP is today considered one of the best means of protection in mixed-status couples, particularly if the HIV-positive partner is also on antiretroviral therapy. In such cases, the risk of transmission can drop to over 90%.

Guidelines for HIV prevention are founded on a few simple principles:

  • Limit your number of sex partners.
  • Consider abstinence, mutual masturbation, or other sexual activities of lower risk.
  • Don't leave anything unspoken. Ask your sex partner about his/her status and/or treatment, and make every effort to disclose your status.
  • Post-exposure prophylaxis(PEP) can reduce the likelihood of transmission if you are accidentally exposed to the virus. The 28-day course of treatment should be started within 36 hours to a maximum of 72 hours.
  • While controversial to some (more often due to personal aversion to the practice),  circumcision in men can potentially reduce the risk of acquiring HIV by anywhere from 50-60%, while having some benefit to the female or receptive male partner. 

Edited by Dennis Sifris, MD and James Myhre


U.S Centers for Disease Control and Prevention. (2015) "HIV Transmission." Atlanta, Georgia, accessed September 24, 2015.

Supervie, V.; Viard, J; Costagliola, D.; et al. "Heterosexual risk of HIV transmission per sexual act under combined antiretroviral therapy: systematic review and Bayesian modelling." Clinical Infectious Diseases. April 19, 2014; pii: ciu223 [Epub ahead of print].

Liu, C.; Hungate, B.; Tobian, A.; et al. "Male Circumcision Significantly Reduces Prevalence and Load of Genital Anaerobic Bacteria." mBio. February 15, 2013; 4(2): e00076-13.

Page-Shafer, K.; Shiboski, C.; Osmond, D.; et al. "Risk of HIV infection attributable to oral sex among men who have sex with men and in the population of men who have sex with men." AIDS. November 22, 2002; 16(17):2350-2352.

Kwakwa, H. and Ghobrial, H. "Female-to-Female Transmission of Human Immunodeficiency Virus." Clinical Infectious Diseases. September 24, 2002; 36 (3):e40-e41.

Smith, D.; Grohskopf, L.; Black, R., et al. "Antiretroviral Postexposure Prophylaxis After Sexual, Injection-Drug Use, or Other Nonoccupational Exposure to HIV in the United States." Morbidity and Mortality Weekly Report. January 21, 2005; 55(RR02):1-20.

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