HIV/AIDS

HIV Transmission, Risk Factors, and Prevention

Joseph Bennington-Castro
By Medically Reviewed by 
Reviewed:
Medically Reviewed
opened condoms on peach background
Use of condoms, among other precautions, can help prevent HIV transmission. In the United States, the virus is mostly spread through unprotected sex or through shared drug equipment.Yaroslav Danylchenko/Stocksy; Everyday Health

When the human immunodeficiency virus (HIV) causes infection, it attacks certain immune system cells called T helper cells, or CD4 cells. The virus replicates itself and, over time, damages its host cells, impairing the body's ability to fight off infections and making it susceptible to other diseases. Acquired immunodeficiency syndrome, or AIDS, is the final stage of an infection with HIV.

Anyone can get HIV, but certain populations are at greater risk. There are, however, a number of ways to reduce your risk, and certain medicines and precautions can prevent the spread of the virus.

How HIV Is Transmitted

To contract HIV, certain bodily fluids infected with the virus must enter your bloodstream directly, or come into contact with damaged tissue or the mucous membranes of your rectum, vagina, opening of the penis, or mouth.

Fluids that can transmit HIV include:

  • Blood
  • Semen ("cum")
  • Pre-seminal fluid ("pre-cum")
  • Rectal fluids
  • Vaginal fluids
  • Breast milk
In the United States, HIV is most commonly transmitted via anal or vaginal sex, or through the sharing of contaminated needles, syringes, or other equipment for the injection of drugs, including heroin, steroids, and hormones.

While the estimated number of HIV infections due to intravenous drug use has remained stable in recent years, the Centers for Disease Control and Prevention (CDC) notes that increased use of injected drugs, as a result of the opioid epidemic, puts new populations at risk of HIV. People who inject drugs accounted for 10 percent of new HIV diagnoses in 2018.

Though less common, the virus can also be transmitted by:

  • An infected mother to her infant through pregnancy, birth, or breastfeeding
  • Oral sex, especially if it involves ejaculation in the mouth
  • Infected blood from mouth sores and bleeding gums, such as through "deep" open-mouth kissing, biting that breaks the skin, and eating food that's been prechewed by an HIV-positive person
  • HIV-contaminated needles and objects that puncture the skin, especially needle-stick injuries in the healthcare setting
  • Blood and clotting factor transfusions, and organ and tissue transplants (because of comprehensive testing, this is mostly an issue outside the United States)
HIV is not transmitted through saliva, sweat, or tears, nor is it spread through social contact (hugging or shaking hands) with someone who is infected.

It is possible that improperly sterilized tattoo or piercing equipment could transmit the virus, but there are no known cases in the United States of someone contracting HIV this way, according to the CDC.

What Are the Risk Factors for HIV?

According to the CDC, your risk of contracting HIV depends on a number of factors.

These include:

Of risks associated with different sex practices, receptive anal intercourse rates the highest — because the lining of the anus is thin, allowing HIV to enter the body — followed by insertive anal intercourse and receptive penile-vaginal intercourse, according to the CDC.

Certain other sexual practices, including oral-anal contact and sharing sex toys, carry very low but not zero risk of HIV transmission.

Demographic Groups With Higher HIV Risk

Though the above risk factors are the same for everyone, HIV affects certain demographic groups more than others.

Bisexual and gay men accounted for about 70 percent of new HIV cases in 2019, according to the CDC.

Additionally, African-Americans accounted for 42 percent of diagnoses in 2019 — the highest percentage of any racial group.

Hispanics and Latinos accounted for 21.7 percent of new cases that same year.
Younger people tend to have the highest HIV diagnosis rates. In 2019, people ages 25 to 34 accounted for about 30 percent of people diagnosed with HIV.

Transgender women who have sex with men are one of the groups at highest risk of contracting HIV, according to HIV.gov. People who use injected drugs are also at increased risk.

What You Can Do to Prevent the Transmission of HIV

There are several steps you can take to reduce your risk of contracting or transmitting HIV. Getting tested is a good start.

If you’re negative, you can take precautions to stay that way, including correctly using barrier methods during sex, such as condoms, and never sharing needles. The CDC recommends limiting the number of your sexual partners to reduce the risk of having a partner who can transmit the virus to you.

RELATED: 8 Things Your Doctor Wants You to Do to Protect Against HIV

Preventive Medicine

If you’re HIV-negative but in a high-risk group for HIV, ask your doctor about preexposure prophylaxis, or PrEP. This consists of taking HIV medication to reduce your risk of HIV prior to becoming infected, and it’s been shown to be highly effective when taken consistently.

PrEP should be considered, for instance, if you’re HIV-negative, but in a relationship with an HIV-positive partner.

PrEP is available in both pill form and as injections.

Truvada and Descovy are both pills that combine the medicines emtricitabine and tenofovir. When taken every day as directed, they have been found to be 99 percent effective in preventing sexual transmission of HIV. It can be difficult, though, for some people to stick to a daily regimen.

In December 2021, the U.S. Food and Drug Administration (FDA) approved the injectable PrEP drug Apretude (cabotegravir extended-release), which is administered once every two months. In clinical trials Apretude was shown to reduce the risk of contracting HIV by 69 percent for cisgender men and transgender women who have sex with men compared with taking the daily PrEP medication Truvada in pill form. For cisgender women at high risk for HIV, the injection reduced the risk of contracting the virus by 90 percent compared with treatment with daily oral Truvada.

A course of antiretroviral medicines (ART) after you've potentially been exposed to HIV can also prevent you from becoming infected; this is called postexposure prophylaxis (PEP). If you’re worried you’ve been exposed, contact your doctor as soon as possible or go to the emergency room. PEP needs to be started within 72 hours to work, but the sooner the better. Every hour counts, according to the CDC.

If you’re HIV-positive, taking ART as directed decreases the amount of the virus in your body, what’s known as viral suppression. Sometimes the viral load is so low, even HIV tests don’t detect it. Being virally suppressed or having an undetectable viral load helps prevent the spread of HIV and is known as “treatment as prevention.”

Those living with HIV who maintain an undetectable viral load have, according to the CDC, effectively have no risk of transmitting the virus to their sexual partners. For pregnant women living with HIV, treatment as prevention (when HIV medicine is taken throughout pregnancy, labor, and delivery, and if HIV medicine is given to the baby for several weeks after delivery) can reduce the risk of transmission to 1 percent or less.

Additional reporting by Deborah Shapiro.

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