We use cookies to give you the best browsing experience. Read more here.
A red illustration of the molecular structure of HIV

Illustrations by Marta Pucci

Sex

HIV: Sexual Transmission, Risk Factors, & Prevention

by Nicole Telfer, Science Content Producer
  • Share this article on Twitter
  • Share this article on Facebook
  • Share this article with WhatsApp

Top things to know

  • HIV is transmitted through the exchange of certain types of bodily fluids including: blood, semen, breast milk, and vaginal fluids
  • Saliva, tears, sneezing, and physical contact cannot transmit HIV
  • Having unprotected anal sex, penis-vagina sex, and even oral sex (though rarely) can transmit HIV
  • There is no cure for HIV, but medications are available which can keep the viral load low and even prevent HIV transmission, as well as others which can greatly reduce the risk of contracting HIV

What is HIV? And what is AIDS?

HIV/AIDS are widely known as incurable sexually transmitted diseases, but you might not know the difference between these acronyms and what they stand for.

For simplicity’s sake, HIV is the virus that causes AIDS. HIV stands for the Human Immunodeficiency Virus.

If a person takes a blood test and receives a diagnosis of HIV, then they are HIV positive—if a person does not have HIV, then they are HIV negative. HIV causes havoc in a person’s body by weakening their immune system (1). HIV progressively destroys the cellular part of the immune system—particularly types of white blood cells called CD4 cells—which, over time, makes the person become immunodeficient (1).

As the HIV infection develops in the body, the person will become more and more immunodeficient until they reach a point where they are classified as having Acquired Immunodeficiency Syndrome (AIDS). This is often the end stage of an HIV infection, where a person’s body is so immunodeficient that they develop infections, diseases, or cancers and are no longer able to mount a immune defense and fight them off (1).

There is no cure for HIV (1). But, if a person does become infected with HIV there are treatments available which can help keep a person healthy.

How is HIV transmitted?

HIV is transmitted between humans through the exchange of certain types of bodily fluids. Bodily fluids that can transmit HIV include blood, semen, breast milk, and vaginal fluids (1).

Not all body fluids can transmit HIV. The following cannot transmit HIV:

  • Exchanging saliva, like through closed-mouth kissing or sharing drinks/utensils
  • Coming in contact with an HIV positive person’s tears, sneezes, or sweat
  • Ordinary physical contact, such as hugging, hand shaking, or touching shared objects like cutlery, cups, or toilet seats (1,2).
  • Air or water (2)
  • Pets and insects (including mosquitoes) cannot carry the virus and infect you, because transmission of HIV is only between humans (2).

While care needs to be taken in some situations—like when having sex or when open injuries are present—this certainly does not mean that it is unsafe to be around people with HIV. Think of how you interact with the vast majority of people—bodily fluids are not exchanged. Harboring discriminatory thoughts only perpetuates a fearful stigma against someone with HIV, which only hurts the person who has it.

HIV is often transmitted through sexual activity and drug use in adults in the United States (2). Maternal transmission—from mother to child—is how the infection is spread to infants (2).

HIV and sex

Knowing which activities put you at a greater risk for acquiring HIV can help you make the best choices for you. This shouldn’t come as a surprise to most adults with a basic grasp of sexual education—HIV is often transmitted through sex.

Having unprotected sex (without a condom or barrier) puts a person at risk for contracting HIV. The best way to avoid contracting HIV is to avoid having any type of unprotected vaginal, anal, or oral sex with anyone who is known to have HIV, or whose HIV status is unknown.

Each type of sexual contact carries its own risk of transmission.

Anal sex

This type of sex has the greatest risk of HIV transmission (2). Both partners who participate in unprotected anal sex are at risk for contracting HIV (and other STIs), but the anal receptive partner is at greater risk. The lining on the inside of the anus is thin and prone to tearing during anal sex, which can allow the virus from semen or blood to enter the body. The insertive partner is also at risk of contracting HIV, as the virus can enter the body through the urethra (the tube where urine exits the body) or any cuts or open-sores on the penis (2). While it is difficult to estimate the rates of transmission for HIV from unprotected anal sex, research suggests that one transmission occurs out of every 72 unprotected receptive anal sex acts (3).

Anal sex is not just limited to men who have sex with men—couples of any gender can enjoy anal sex. To prevent the spread of HIV, always use a condom when having anal sex.

Penis-vagina sex

Like anal sex, having unprotected penis-in-vagina sex can transmit HIV to either partner. The vagina, much like the anus, is also made of soft tissue and can become irritated during sex, which can allow HIV from semen, pre-cum, or blood to enter the body. One out of every 1250 unprotected penis-vagina sexual acts will result in contracting HIV for the receptive person (3). While this number may seem low, many factors can affect and increase this rate of transmission.

People with penises can contract HIV from having penis-in-vagina sex from vaginal fluids or blood, through the urethra or any cuts or open-sores on the penis (2), though this transmission happens only half as often (3). Using a condom protects both people.

Oral sex

Although very rare, it is possible to transmit HIV through oral sex. If a person giving the oral sex has open sores in their mouth which come in contact with semen, sexual fluids, or blood, then they could contract HIV (2). To prevent the transmission of HIV and other STIs during oral sex, always be sure to use a condom or barrier method.

Open mouth kissing

HIV cannot be spread through saliva. In the very rare case that both partners have bleeding cuts or open sores in their mouths, then theoretically this could transmit HIV (2).

Vulva-vulva sex

This type of HIV transmission is rare, but not impossible. Vaginal fluids and menstrual blood can both transmit the HIV virus (2).

HIV and drugs

Using injectable drugs can put you at risk for contracting HIV. Getting counselling and/or medical help to stop using drugs is the best way to decrease the risk of being infected. Be sure to reach out to a healthcare practitioner, family member, friend, or local substance abuse treatment center for help.

Dirty needles

Injecting drugs using a previously used needle, equipment, or solution, can expose someone to HIV. It is important to always use clean, sterile, never-used equipment when injecting drugs, and never share needles (2). If a person is not ready to stop using drugs and is unable to purchase clean needles, many communities offer needle-exchange programs. After injecting, always be sure to dispose of used needles properly.

“High” sex is risky sex

People who are high are more likely to engage in risky sex (without a condom) (2). This puts a person at greater chance of being exposed to HIV.

HIV and maternal transmission

HIV can be passed from mother to child during pregnancy, delivery, or through breastfeeding. If left untreated throughout these stages, there is a 15-45% chance of an HIV positive mother transmitting the virus to their child (1). However there are treatment options to prevent this from happening.

If pregnancy occurs and there has been potential HIV exposure, ask a healthcare provider about getting tested for HIV as early as possible. Taking medications called antiretroviral therapy (ART) as prescribed can reduce the viral load so that the baby has a very low (less than 1%) chance of contracting HIV (4).

A person with HIV should not breastfeed their child, as breast milk can transmit HIV. Even if a person is taking ART and their viral loads are undetectable, they should still not breastfeed.

HIV Prevention and Treatment

Viral load & medications

If someone has HIV, this does not mean that they are restricted to celibacy. Many people with HIV still continue to have safe, enjoyable sex lives without spreading the virus. Always using a condom or barrier method is an important first step to prevent the sharing of HIV containing fluids.

Antiretroviral therapy (ART): Another way to help decrease the risk of spreading HIV is to lower a person’s viral load—the amount of HIV in a person’s blood. Viral loads can be lowered using medications called antiretroviral therapy (ART). These medications can lower the HIV viral load so much that HIV may not even be detectable on a blood test—this is called an undetectable viral load (4). When a person's viral load in undetectable, they have effectively no risk of transmitting the HIV virus to a non-infected partner (4). Taking these medication will help keep a person with HIV healthy while also helping prevent the spread of HIV to another person. This is not a cure, however. If medication is taken incorrectly or stopped, HIV viral loads will increase again and transmission can occur. Condoms and other barrier methods should still always be used during sex (4).

If you have HIV and have an undetectable viral load, you should still tell your partner before having sex.

Post-exposure prophylaxis (PEP): If there has been a possible exposure to HIV (for example, if a condom broke during sex with someone who has HIV), seek medical help immediately. Medications called post-exposure prophylaxis (PEP) are available which decrease the chances of getting HIV. These medications need to be started within 72 hours of exposure and taken for about a month (4).

Pre-exposure prophylaxis (PrEP): Medication called pre-exposure prophylaxis (PrEP) can be taken daily to decrease the risk of contracting HIV if exposed (4).

Get treatment for sexually transmitted infections (STIs)

Sexually transmitted infections (STIs) increase the chance of both spreading and contracting HIV. If a person has HIV and another STI, that person has greater the chance of transmitting HIV, as opposed to a person who only has HIV but no other STI (2).

This works both ways—a person who does not have HIV but does have another STI has a greater chance of contracting HIV if they have unprotected sex with someone who has HIV (2). This is because STIs that cause open sores or irritation which breaks the skin’s barrier (like syphilis, genital herpes, HPV, or chancroid) provide an entrance for HIV to enter the body during all types of unprotected sex (2).

Other STIs that don’t cause openings in the skin (like chlamydia, gonorrhea, and trichomoniasis infections) can still increase the risk of contracting HIV. This is because STIs cause inflammation to the genital area, drawing in more immune cells to the area, which are the target for HIV (2).

Lube can make sex fun and safer

Using lube isn’t just for enhancing sexual fun—it’s can also make sex even safer. Using lube helps to decrease the friction between skin and/or condom, which provides enjoyably smooth gliding movements and decreases the rate of condom breaking, or tearing during anal sex (5). Water-based lubes and silicone-based lubes are both safe to use with female and male condoms. However, oil-based lubes (or any other oil products like petroleum jelly or mineral oil) should not be used with latex condoms, as they can dissolve the latex of the condom and may cause latex condoms to break (4).

Penile circumcision

Penile circumcision is the surgical removal of the foreskin from a penis. This is a common procedure, which is often performed as an elective choice on babies for cultural or religious reasons. Sometimes circumcisions are performed to treat medical conditions, and recently circumcision has been advocated for disease prevention.

There is a link between circumcision and rates of HIV contraction. People with circumcised penises are less likely to contract HIV from an HIV positive person during penis-vagina sex (1,4). For this reason, some governments in Africa where HIV prevalence is high, along with the World Health Organization (WHO), recommend that boys and men who do not often have access to healthcare services have voluntary medical male circumcision (VMMC) as an additional way to decrease the spread of HIV (1). Being circumsized does not eliminate the chance of contracting HIV; it only decreases it—so condoms should still always be used.

HIV is not the death sentence it used to be. With advances in modern treatment and preventive care, rates of HIV infection, AIDS, and related deaths are decreasing overall (1). But there is still a long way to go, with the World Health Organization predicting that there are close to 37 million people in the world living with HIV (1). Prevention, safer sex, accessible STI testing, and treatment are critical to stopping the spread of HIV.

Download Clue to track protected and unprotected sex.

You might also like to read