What Is the Risk of HIV From Vaginal Sex?

Multiple vulnerabilities increase risk in men and women

Vaginal sex between partners is one of the most common ways a person can acquire HIV. Both women and men can be put at risk when they have vaginal sex without using a condom.

There are a number of risk factors shared by both partners. There also are reasons for why men may be at risk, and other reasons for why women may be far more likely to become infected with HIV.

This article discusses why vaginal sex presents an HIV risk for both men and women. It explains why anatomical differences, cultural norms, and even how well HIV treatment works can affect that risk.

heterosexual couple's legs intertwined in bed

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Sex and Gender Identity

This article refers to men and women in its discussion of vaginal sex and HIV risk. These terms describe sex assigned at birth. Vaginal sex means sex between a person with a penis and a person with a vagina. At Verywell Health, we respect that there are many ways a person may hold and express a sense of gender identity.

Risk by Sexual Activity

In the U.S., vaginal sex accounts for some 5,300 new infections each year among women. There are about 2,400 new infections in men who have sex with women, although the vast majority of the 34,800 new cases occur in men who have sex with other men.

To be sure, the HIV transmission rates have improved over the years. But much of the drop in overall cases is seen in men, while progress for women remains stalled.

At the global scale, heterosexuals are by far the group most affected. For example, in African nations, vaginal sex is the most likely route of HIV infection.

When discussing HIV risk, people often look at which "type" of sex is riskier. They compare vaginal, anal, and oral sex. Based entirely on the numbers, anal sex is considered the highest risk activity. The risk of HIV infection is almost 18 times greater with anal sex than it is for vaginal sex.

Statistics are not individual people. It's true that vaginal sex may pose an overall “lower” risk when compared with anal sex. What the data can't tell you is how the risk of HIV infection may differ among men and women who practice vaginal sex.

The data on risk doesn't always explain factors that make some people more vulnerable. It doesn't consider how these factors cause HIV infection risk to be much higher than it is for other people.

Women are about twice as likely to develop an HIV infection than men are when engaged in a heterosexual act. A woman is more likely to get HIV from her first sexual encounter with a man than her male partner is.

Some men are far more likely to get HIV than other men are. Studies suggest uncircumcised men are more than twice as likely to get HIV after vaginal sex than circumcised men.

Recap

Vaginal sex is not the riskiest practice for HIV infection. Yet it still presents a risk to both partners, with that risk being greater for women than it is for men. This is due to several factors, including vulnerabilities that place women (and some men) at greater risk than others.

Risk Factors in Women

The HIV risk from vaginal sex without condom use is higher among women for a number of reasons. Chief among them are the ways that women's bodies are different from men's.

Normally, the body's immune system recognizes and responds to an invading virus. Instead, HIV reverses its mission. The CD4 T-cells meant to help neutralize the threat are instead attacked. This means the body supports its own infection instead of fighting it.

The epithelial tissue that lines the vagina is far more susceptible to HIV than those of the penis. HIV is able to pass through these tissues.

The surface area of these vaginal tissues is far greater than that of the urethra, the thin tube that runs through the penis and connects to the bladder. For this reason, the chances of HIV infection are much higher in women.

Other vulnerabilities based on differences between men and women include:

  • The cells of a woman's cervix, at the opening of the uterus, are especially vulnerable to HIV. This is especially true during adolescence or a first pregnancy. It's also true if you have a sexually transmitted infection (STI) like chlamydia or human papillomavirus (HPV).
  • Women with a genital tract infection, whether from bacteria, a virus, or a fungus, are at increased risk for HIV. Some studies have suggested that bacterial vaginosis is associated with an eight-fold increase in risk. That's a 1 in 100 chance of getting HIV during vaginal intercourse.
  • Sex without condom use can increase HIV risk in a woman if the man ejaculates semen into her vagina. Key factors that affect the risk include how long you are exposed and how much infected fluid there is.
  • Open sores or ulcers from STIs like syphilis can increase risk in both men and women. In women, however, the sores are less visible than they are on a man's penis. They may go unnoticed.
  • Douching practices may alter the vagina's "good" bacterial flora, though this is still under debate.

The daily use of an HIV drug called pre-exposure prophylaxis (PrEP) can reduce the risk of HIV in an uninfected partner. There is evidence, however, that it works less well in women.

Research models developed from a study of 49 women in 2016 suggest the level of the active drug molecule in vaginal tissue isn't nearly as high as when it is used in the rectal tissue of men who have sex with men.

There are social vulnerabilities that can place women at increased risk too. They include sexual violence in relationships. In these cases, women are limited in protecting themselves and the chance of damage to delicate vaginal tissue is higher.

Poverty, social norms, and gender imbalances all may contribute to male privilege in relationships. A man's dominance in other areas likely extends into the bedroom as well. All of these factors may contribute to higher rates of HIV in women.

Recap

Much of the reason that HIV infection risk is greater for women is due to anatomy. Tissues in the vagina are more easily infected than those in a man's penis. A woman is the receiving partner of fluids that are more likely to cause infection. Social factors also may place women at a greater risk than their male partners.

Risk Factors in Men

The fact that men are less susceptible to HIV than women shouldn't underplay the fact that as individuals, they may still be at a higher risk for HIV infection.

For example, the uncircumcised penis still has a foreskin that's intact. This makes it easier for bacteria to be trapped beneath it and lead to an infection. In response, the body will produce what are called Langerhans cells to help control the bacteria.

When a man has condomless sex with an HIV-positive woman, Langerhans cells work to transport the virus to CD4 T-cells to have it destroyed. But with HIV, this may actually boost the chance of HIV infection. STIs and genital tract infections can further increase the risk of HIV.

In many societies, the cultural norms for what it means to be men encourage sex. Sexual adventure is viewed as an expression of masculinity. As a result, men may have more sexual partners than women and engage in behaviors that raise the risk of HIV.

Shared Vulnerabilities

Both men and women share some of the same vulnerabilities when it comes to HIV infection.

For example, drinking alcohol or taking drugs can affect the ability to make safe choices in both men and women. This may lead to sex without condoms, or alter a person's ability to stick to their HIV drug therapy.

If the infected partner of either sex has an increased amount of HIV in the blood (viral load), this raises the risk for the HIV-free partner. A high viral load during acute infection, which comes right after exposure, is associated with an increase in HIV transmission risk.

On the other hand, people with viral loads too low to detect are not able to transmit HIV to a partner through sex.

Recap

Uncircumcised men have a higher risk of HIV infection through vaginal sex. Men also may engage in more risky behaviors. Alcohol and drug use may lead to more risk for both men and women. These choices also may affect viral load in an HIV-positive partner under treatment, and raise the risk of transmission.

Per-Exposure Risk

One way to measure HIV risk is based on what's called "per-exposure risk." This risk can vary based on gender, the viral load of the HIV-positive partner, and even the part of the world you live in.

For example, the per-exposure risk for women who have vaginal sex with men is eight in 10,000 such sexual acts. The risk is four in 10,000 for men. That may seem low, but these statistics do not reflect the reality that having vaginal sex without protection, even once, can lead to HIV infection.

Keep in mind that per-exposure risk numbers do not take into account any other factors that can increase risk. These factors include:

  • Presence of an STI
  • Injection drug use
  • Underlying infection such as hepatitis C

Accidental Exposure Risk

Medications called post-exposure prophylaxis (PEP) can greatly reduce your risk of infection if you think you may have been exposed to HIV. PEP consists of a 28-day course of antiretroviral drugs, which must be taken completely and without interruption.

PEP must be started as soon as possible​ideally within 36 hours of exposurein order to minimize the risk of infection.

Summary

Vaginal sex, between a person with a penis and a person with a vagina, presents the risk of HIV infection. For a number of reasons, that risk is greater for women than it is for men.

Much of the difference in HIV risk is because of the difference in men's and women's bodies. The vagina is more vulnerable to infections than the penis. It also receives fluids that may carry HIV infection during vaginal sex. Social and cultural factors also may play a role.

Uncircumcised men also have a higher risk of HIV infection through vaginal sex. Both sexes are at greater risk when, for example, alcohol and drug use alter their decision-making about safer sex practices or their ongoing HIV treatment.

A Word From Verywell

A healthy sex life is possible when both partners take the proper precautions. That's true even when living with HIV infection. Correct condom use and, in some cases, HIV treatment drugs can prevent transmission during vaginal sex. Be sure to discuss any concerns with your healthcare provider.

Frequently Asked Questions

  • What's the HIV Risk for Behaviors Other Than Sex?

    The highest HIV transmission risk comes from blood transfusion, at 9,250 cases per 10,000 procedures. By comparison, sharing needles when using drugs is at 63 per 10,000 and accidental needle sticks are 23 per 10,000.

  • What age group has the highest risk of HIV infection?

    In 2019, the number of new HIV infections was highest for people ages 25 to 29. HIV diagnoses increased for people ages 13 to 24 years, 35 to 44 years, and 45 to 54 years. At any age, good information can help you to cope with a new diagnosis.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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