HIV 101: How is HIV Transmitted?

Know your risks about transmitting and contracting HIV

HIV 101: How is HIV Transmitted?

  • 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

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, 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 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— 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 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

anal sex, having unprotected penis-in-vagina sex can transmit HIV to either partner.

The vagina, much 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 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 ly 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.

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 ( 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 ( 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 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 ly 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.



HIV 101: How is HIV Transmitted?

The human immunodeficiency virus (HIV) targets the immune system and weakens people's defense against many infections and some types of cancer that people with healthy immune systems can fight off. As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. Immune function is typically measured by CD4 cell count.

The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which can take many years to develop if not treated, depending on the individual. AIDS is defined by the development of certain cancers, infections or other severe long-term clinical manifestations.

Signs and symptoms

The symptoms of HIV vary depending on the stage of infection. Though people living with HIV tend to be most infectious in the first few months after being infected, many are unaware of their status until the later stages. In the first few weeks after initial infection people may experience no symptoms or an influenza- illness including fever, headache, rash or sore throat.

As the infection progressively weakens the immune system, they can develop other signs and symptoms, such as swollen lymph nodes, weight loss, fever, diarrhoea and cough. Without treatment, they could also develop severe illnesses such as tuberculosis (TB), cryptococcal meningitis, severe bacterial infections, and cancers such as lymphomas and Kaposi's sarcoma.


HIV can be transmitted via the exchange of a variety of body fluids from infected people, such as blood, breast milk, semen and vaginal secretions.

HIV can also be transmitted from a mother to her child during pregnancy and delivery.

Individuals cannot become infected through ordinary day-to-day contact such as kissing, hugging, shaking hands, or sharing personal objects, food or water. 

It is important to note that people with HIV who are taking ART and are virally suppressed do not transmit HIV to their sexual partners.  Early access to ART and support to remain on treatment is therefore critical not only to improve the health of people with HIV but also to prevent HIV transmission.

Behaviours and conditions that put individuals at greater risk of contracting HIV include:

  • having unprotected anal or vaginal sex;
  • having another sexually transmitted infection (STI) such as syphilis, herpes, chlamydia, gonorrhoea and bacterial vaginosis;
  • sharing contaminated needles, syringes and other injecting equipment and drug solutions when injecting drugs;
  • receiving unsafe injections, blood transfusions and tissue transplantation, and medical procedures that involve unsterile cutting or piercing; and
  • experiencing accidental needle stick injuries, including among health workers


HIV can be diagnosed through rapid diagnostic tests that provide same-day results. This greatly facilitates early diagnosis and linkage with treatment and care. People can also use HIV self-tests to test themselves.

However, no single test can provide a full HIV diagnosis; confirmatory testing is required, conducted by a qualified and  trained health or community worker at a community centre or clinic.

HIV infection can be detected with great accuracy using WHO prequalified tests within a nationally approved testing strategy.

Most widely-used HIV diagnostic tests detect antibodies produced by the person as part of their immune response to fight HIV. In most cases, people develop antibodies to HIV within 28 days of infection.

During this time, people experience the so-called “window” period –  when HIV antibodies haven’t been produced in high enough levels to be detected by standard tests and when they may have had no signs of HIV infection, but also when they may transmit HIV to others.

After infection, an individual may transmit HIV transmission to a sexual or drug-sharing partner or for pregnant women to their infant during pregnancy or the breastfeeding period.

Following a positive diagnosis, people should be retested before they are enrolled in treatment and care to rule out any potential testing or reporting error. Notably, once a person diagnosed with HIV and has started treatment they should not be retested.

While testing for adolescents and adults has been made simple and efficient, this is not the case for babies born to HIV-positive mothers.

For  children less than 18 months of age, serological testing is not sufficient to identify HIV infection – virological testing must be provided as early as birth or at 6 weeks of age.

New technologies are now becoming available to perform this test at the point of care and enable same-day results, which will accelerate appropriate linkage with treatment and care.


Individuals can reduce the risk of HIV infection by limiting exposure to risk factors. Key approaches for HIV prevention, which are often used in combination, include:

  • male and female condom use;
  • testing and counselling for HIV and STIs;
  • testing and counselling for linkages to tuberculosis (TB) care;
  • voluntary medical male circumcision (VMMC);
  • use of antiretroviral drugs (ARVs) for prevention;
  • harm reduction for people who inject and use drugs; and
  • elimination of mother-to-child transmission of HIV.

HIV disease can be managed by treatment regimens composed of a combination of three or more antiretroviral (ARV) drugs.

Current antiretroviral therapy (ART) does not cure HIV infection but highly suppresses viral replication within a person's body and allows an individual's immune system recovery to strengthen and regain the capacity to fight off opportunistic infections and some cancers.

Since 2016, WHO has recommended that all people living with HIV be provided with lifelong ART, including children, adolescents, adults and pregnant and breastfeeding women, regardless of clinical status or CD4 cell count. 

By June 2021, 187 countries had already adopted this recommendation, covering 99% of all people living with HIV globally.

In addition to the treat all strategy, WHO recommends a rapid ART initiation to all people living with HIV, including offering ART on the same day as diagnosis among those who are ready to start treatment.

By June 2021, 82 low- and middle-income countries reported that they have adopted this policy, and approximately half of them reported country-wide implementation.

Globally, 27.5million [26.5–27.7 million] people living with HIV were receiving ART in 2020. This equates to a global ART coverage rate of 73% [56–88%]. However, more efforts are needed to scale up treatment, particularly for children and adolescents. Only 54% [37–69%] of children (0–14 years old) were receiving ART at the end of 2020.

The Sixty-Ninth World Health Assembly endorsed the “Global health sector strategy on HIV for 2016–2021”. The strategy includes five strategic directions that guide priority actions by countries and by WHO over six years.

The strategic directions are:

  • Information for focused action (know your epidemic and response)
  • Interventions for impact (covering the range of services needed)
  • Delivering for equity (covering the populations in need of services)
  • Financing for sustainability (covering the costs of services)
  • Innovation for acceleration (looking towards the future).

WHO is a cosponsor of the Joint United Nations Programme on AIDS (UNAIDS). Within UNAIDS, WHO leads activities on HIV treatment and care, and HIV and TB coinfection, and jointly coordinates the work on elimination of MTCT of HIV with UNICEF.

  • Global health sector strategy on HIV, 2016-2021
  • Consolidated HIV strategic information guidelines


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