What to know about HIV transmission

Share on Pinterest

In most instances, people contract HIV through anal or vaginal sex or by sharing drug injection equipment, such as needles or syringes.

HIV can only pass on through certain body fluids:

• blood
• semen
• pre-ejaculate
• rectal fluids
• vaginal fluids
• breast milk

Blood can carry more of the virus than other bodily fluids. Therefore, the greatest likelihood of transmission involves exposure to blood containing the virus.

However, HIV does not pass on through all contact with fluids carrying the virus. For transmission to occur, the fluid must come into contact with damaged tissue, the bloodstream, or mucous membranes, such as those in the genitals, rectum, or mouth.

If blood containing HIV comes into direct contact with another person’s bloodstream, such as through an injection with a shared needle, this is very likely to transmit the virus.

HIV can pass to a baby during pregnancy, birth, or nursing. However, this is less common due to modern preventive measures and treatments.

According to the Centers for Disease Control and Prevention (CDC), HIV is not transmissible through:

• insect bites, including those from mosquitoes and ticks
• the air
• contact with saliva, tears, or sweat
• shaking hands, hugging, or closed-mouth kissing
• sharing toilets, dishes, or utensils
• eating food that someone with HIV has handled or prepared
• sexual activities that do not involve fluid exchange, such as touching

HIV cannot survive long outside the body, so it does not transmit via surfaces.

Additionally, the risks of contracting the virus through other methods of exposure, such as biting, scratching, and throwing bodily fluids, are either very small or nonexistent.

There is also little to no risk of contracting HIV via:

• Oral sex: However, having mouth ulcers, genital sores, or bleeding gums can increase the risk of transmission, as can having existing sexually transmitted infections (STIs).
• Workplace exchanges: However, a puncture from a needle or another sharp object that contains the virus can lead to transmission.
• Blood transfusion or donated organs: Current screening practices in the United States are safe and undergo stringent regulation, making this transmission highly unlikely.
• Deep, open-mouth kissing: Transmission in this way is very rare, but it can occur if both people have oral sores or bleeding gums.
• Tattoos and body piercings: There have been no reports of transmission from tattoos or piercings in the United States, although it is possible if the equipment or ink has been in contact with someone else’s blood.

Anyone can contract HIV, but several factors increase the risk. These include:

• sharing equipment for injecting drugs
• getting a tattoo with a shared needle or shared ink
• having anal or vaginal sex without a condom
• having an STI
• having frequent exposure to fluids containing the virus, such as in laboratory, medical, or emergency settings
• using drugs and alcohol, which can impair judgment
• having exposure to the virus during childbirth, pregnancy, or nursing

HIV affects certain U.S. populations more than others, including:

• Black and Latinx people
• cisgender and transgender males who have sex with cisgender males
• transgender females

In 2021, the latest year for which figures are available, males who had sex with other males received 67% of all new HIV diagnoses in the United States. Anal sex without a condom was the most likely route of transmission as the risk of tissue damage is high.

HIV also affects more people who are Black or Latinx due to systemic inequity in healthcare and social and economic marginalization, as well as other ingrained barriers.

In 2021, Black people received 40% of new HIV diagnoses in the United States, while Hispanic and Latino individuals received 29% of those diagnoses, and white people received 25%.

The prevalence of HIV differs by U.S. region. In 2021, the South had the largest number of people living with HIV. However, in terms of its population size, the Northeast had the largest rate of individuals living with HIV.

What about breastfeeding or chestfeeding?

According to the World Health Organization (WHO), a person who has acquired HIV and receives no treatment has a 15–45% risk of passing on the virus to their infant during labor, delivery, or nursing. This is due to contact with relevant body fluids.

Antiretroviral therapy can reduce the chances of transmission to below 2% during pregnancy. However, nursing while receiving antiretroviral therapy is not advisable in the United States, according to the CDC.

Social factors

Some social factors that influence a person’s risk of HIV transmission include:

• access to education about HIV transmission and prevention
• access to affordable healthcare
• discrimination and stigma in healthcare and society at large
• reduced negotiating power due to sex, gender, and financial or other status factors

Increased awareness of and access to antiretroviral therapy, preventive medication, and support services are effective ways to reduce the effects of HIV.

A range of effective strategies can now lower the risk of contracting HIV. These include:

• using preexposure prophylaxis (PrEP), a preventive drug
• never sharing needles with another person
• using condoms during sex
• getting frequent HIV testing as per CDC recommendations
• using gloves and other sterile equipment in medical settings
• taking emergency postexposure prophylaxis after possible exposure to the virus

When a person takes PrEP daily, it reduces the risk of contracting HIV via sex by about 99% and via needles and syringes by about 74%.

The Preventive Services Task Force updated its HIV guidelines in 2023. These guidelines recommend PrEP to all people at high risk of exposure to HIV or at high risk of acquiring HIV.

Anyone with HIV who is pregnant or plans to conceive should discuss ways to mitigate the risk of transmission with a healthcare professional, including the choice of whether to breastfeed or chestfeed.

Due to advances in prevention and treatment, the number of new HIV cases in the United States has decreased by more than two-thirds since the mid-1980s.

Undetectable equals untransmittable

Using antiretroviral therapy consistently as a doctor prescribes can reduce the risk of transmission to virtually zero. It slows or stops the activity of HIV in the body.

Health experts consider the virus suppressed when someone with HIV has a viral load of 200 copies per milliliter of blood or under. It may be undetectable at this level or under, meaning it cannot transmit to others. However, it is important to keep following a treatment plan and attend regular check-ups to ensure that the viral load remains undetectable.

Many people with HIV experience no symptoms. A person can only know their HIV status by taking a test.

The CDC recommends that everyone ages 13–64 years have at least one HIV test.

Early testing, diagnosis, and treatment are the most effective ways to stop the progression and transmission of the virus.

Frequent testing is an inexpensive and effective way to stop the spread of HIV. It is especially important to test:

• when planning to become pregnant
• after becoming pregnant
• before having sex with a new partner

People with a high risk of contracting the virus, including gay and bisexual males who are sexually active and sex workers, may wish to undergo testing every 3–6 months.

Individuals should undergo testing once a year or more if:

• their partners have HIV
• they share drug injection equipment with others
• have had hepatitis, tuberculosis, or an STI

What are the odds of contracting HIV?

The CDC provides a risk estimation tool featuring up-to-date evidence in its analysis. It helps a person determine their risk of contracting HIV from various activities.

Below are some commonly asked questions about HIV transmission.

How quickly can HIV be transmitted?

HIV can be transmitted as quickly as having one sexual encounter that leads to exposure to HIV or sharing needles on one occasion with someone living with HIV.

What is considered an open wound for HIV transmission?

HIV transmission can occur via any open cuts or sores and mucus membranes, which include the rectum, vagina, mouth, or tip of the penis.

How much blood is needed to transmit HIV?

The amount of blood needed to transmit HIV is not easily quantifiable. This is because it depends on various factors, including the viral load of the person with HIV, the type of exposure, and the susceptibility of the recipient.

However, HIV transmission typically requires a sufficient quantity of infected bodily fluids, such as blood, to enter the bloodstream of the other person.

In the context of blood transfusions or needle-sharing, even a small amount of blood with a high viral load can pose a risk of transmission.

Can you still have sex with HIV?

A person with HIV can still have sex. To protect their partner, a person should take HIV medication, which can effectively make the virus undetectable. Using a condom during sex is also highly effective in preventing HIV.

HIV is only transmissible in certain situations, such as through contact with blood, rectal fluids, vaginal fluids, breast milk, and semen or pre-ejaculate.

There are several ways to reduce the risk of contracting HIV, including using condoms when having sex, taking PrEP, and never using shared needles.

In the United States, HIV has had a disproportionate effect on certain groups, including Black and Latinx people and cisgender and transgender males who have sex with cisgender males.

However, with modern antiretroviral therapy, fewer people contract HIV. Those with continuous access to this treatment are able to live long, healthy lives, and the risk of transmission is significantly reduced, often to zero.

Read this article in Spanish.