Human immunodeficiency virus (HIV) is a virus that attacks the immune system. One person can transmit HIV to another under certain circumstances.

Understanding the facts about HIV transmission can prevent both the spread of misinformation and the transmission of HIV.

HIV may be transmitted through certain bodily fluids that are capable of containing high concentrations of the virus. These fluids include:

  • blood
  • semen
  • vaginal secretions
  • rectal secretions
  • breast milk

Amniotic and spinal cord fluids can also contain HIV and could pose a risk to healthcare personnel who are exposed to them. Other bodily fluids, such as tears, saliva, and sweat, do not transmit the virus.

How is HIV transmitted from person to person?

HIV is transmitted when a person who has measurable amounts of the virus in their body pass fluids directly into the bloodstream or through mucous membranes, cuts, or open sores of a person without HIV.

Let’s explore the most common ways that HIV is transmitted.


HIV exposure can occur during sexual intercourse. Both anal sex and vaginal sex have risks of HIV transmission.

Receptive anal sex has the highest risk of transmission among sexual activity.

There may be a number of reasons, including that bleeding is more likely during anal sex due to the fragile tissues that line the anus and anal canal. This allows the virus to enter the body more easily even if visible bleeding isn’t observed, as breaks in anal mucosa may be microscopic.

While vaginal sex possibly carries less risk of transmission than anal sex, either partner can contract HIV in this way. According to the Centers for Disease Control and Prevention (CDC), most people with a vagina who contract HIV get it from vaginal sex.

Sharing injection drug equipment

Sharing needles for injecting drugs most efficiently transmits HIV. This is because used needles and syringes can still contain blood, which can carry the virus.

An older study found that HIV can survive up to 42 days in syringes, depending on the temperature.

HIV isn’t the only virus that can be transmitted by sharing injection drug equipment. The viruses that cause hepatitis B and hepatitis C can be transmitted in this way as well.

There are also some less common ways that HIV can be transmitted. Let’s take a look at some of them below.

Is female-to-male HIV transmission unlikely?

Generally speaking, female-to-male (or more accurately, someone with a vagina transmitting the virus to someone with a penis) transmission is less likely than male-to-female transmission.

In fact, it’s estimated that the risk of HIV transmission per heterosexual act is twofold higher for women than for men. However, that doesn’t mean that female-to-male transmission can’t occur.

Some factors can increase the risk of someone with a penis contracting HIV via vaginal sex. For example, open cuts, sores, or ulcers around the penis can provide a way for the virus to enter the body.

There’s also some evidence that circumcision may reduce the risk of HIV. The results from two clinical trials have found that the likelihood of contracting HIV was lower in men who had been circumcised than those who hadn’t.

What about female-to-female transmission?

Female-to-female (or between two people with vaginas) transmission of HIV has been reported, but it’s generally believed to be less likely. This type of transmission can potentially occur due to exposure to vaginal fluids or menstrual blood.

Oral sex

There have been reported cases of HIV transmission via oral sex. Given current research reports, the risk of HIV transmission from oral sex is believed to be very low, but not zero.

Some factors that may increase the risk of HIV transmission through oral sex include:

  • open sores in the mouth or on the genitals
  • bleeding gums
  • having other types of sexually transmitted infections (STIs)

Blood transfusions and organ donation

The risk of contracting HIV from a blood transfusion, other blood products, or organ donation is now extremely rare in the United States. All donated blood or blood products in the United States are tested for several types of bloodborne pathogens, including HIV.

Blood donations that test positive for HIV are safely discarded and don’t enter the blood supply. The risk of HIV transmission during a blood transfusion is conservatively estimated to be 1 in 1.5 million, according to the CDC.

Organ donations are also screened for HIV. Although very rare, it’s possible for HIV transmission to occur following an organ transplant.

However, testing of organ recipients postsurgery can quickly detect transmission so that antiretroviral medications can be started promptly.

Pregnancy and breastfeeding

HIV can also be transmitted from a pregnant person to their child during pregnancy, delivery, and through breastfeeding. However, testing of all pregnant people for HIV has greatly decreased the number of babies that contract HIV in this way.

Additionally, if both the birthing parent and child receive HIV medications during pregnancy and breastfeeding, the risk of transmission can almost be eliminated, according to the World Health Organization (WHO).

Deep, open-mouth kissing

While very rare, it’s possible for HIV to be transmitted by deep, open-mouth kissing.

While the virus can’t be transmitted by saliva, transmission can occur if blood is present. This can happen when both partners have bleeding gums or open cuts or sores in their mouths.

Tattoos and piercings

According to the CDC, there are no known instances of HIV being transmitted by receiving a tattoo or piercing. However, it’s technically possible for transmission to occur if equipment or ink is reused or shared.

Occupational exposures

HIV may be transmitted through accidental occupational injuries, such as cuts and needle sticks.

Healthcare personnel are most at risk for this type of transmission, but the likelihood is very low. It’s estimated that the risk of transmission from these types of exposures is about 0.3 percent.

Bites that break the skin

A bite that opens the skin and causes bleeding can lead to the transmission of HIV. However, according to the CDC, there have been very few cases of a human bite causing enough trauma to the skin to transmit HIV.

Having a detectable or measurable viral load can be a risk factor of HIV transmission. Viral load is the amount of virus that can be detected in the blood. The rate of HIV transmission goes up with increasing viral load.

Viral load is highest both during the early (acute) phase of HIV and without treatment with antiretroviral medications. Taking antiretroviral medications every day can reduce a person’s viral load to very low levels that can’t be detected through testing.

In this way, antiretroviral medications aren’t only a treatment, but an important tool for prevention. When HIV can’t be detected in the blood, a person living with HIV can’t sexually transmit the virus to a partner without HIV.

This principle is called Undetectable = Untransmittable (U = U) and has been supported by several large-scale studies.

It can take up to 6 months of taking antiretroviral medications each day to achieve an undetectable viral load.

A person’s viral load is said to be “durably undetectable” when all test results are undetectable for at least 6 months after the first undetectable result.

There’s no need to be afraid of having casual contact with someone who is living with HIV. The virus doesn’t live on the skin and can’t live very long outside of the body.

Additionally, bodily fluids like saliva, tears, and sweat don’t transmit HIV either.

Therefore, casual contact, such as holding hands, hugging, or sitting next to someone who has HIV, won’t transmit the virus. Closed-mouth kissing isn’t a threat either.

Scratching and spitting also aren’t transmission methods for HIV. A scratch typically doesn’t lead to an exchange of bodily fluids. A bite that doesn’t break the skin can’t transmit HIV either.

Lastly, biting insects like mosquitoes and ticks can’t transmit HIV. This is because the virus is killed in their digestive tracts.

There are several population-, behavior-, and health-related factors that may put a person at increased risk for HIV. These include:

  • engaging in anal or vaginal sex without a condom or other barrier method
  • having sex with multiple or anonymous partners
  • sharing injection drug equipment
  • having other STIs
  • receiving injections or other medical procedures with unsterile equipment

Additionally, there are several groups that the CDC has identified as currently making up a larger number of new HIV cases in the United States based on their population numbers. This can mean a bigger risk factor within these groups.

These include:

  • men who have sex with men (MSM)
  • African Americans
  • Latinos
  • people who use injection drugs
  • transgender people

However, it’s important to remember that HIV can affect anyone, regardless of race, gender, or sexual orientation.

Having an STI can increase the risk of HIV transmission. Some examples of STIs include:

There are a couple reasons that STIs can raise HIV risk. First, the symptoms of many STIs cause genital inflammation, sores, or ulcers to occur. These can all facilitate the transmission of the virus from one person to another.

Second, like HIV, transmission of STIs is associated with some of the same types of behaviors, such as engaging in sex without a condom or other barrier method.

Some research has also indicated that certain STIs may be more closely linked with HIV transmission than others. These STIs include:

  • syphilis
  • gonorrhea
  • herpes

To prevent transmission of both HIV and other STIs, always use a barrier method during vaginal, anal, or oral sex.

Keep open lines of communication with sexual partners, such as discussing the risks associated with sex without a barrier method and sharing STI status.

HIV is most commonly transmitted through anal and vaginal sex and the sharing of injection drug equipment.

Examples of less common routes of transmission include oral sex and transmission during pregnancy.

HIV is not transmitted through things like casual contact or closed-mouth kissing.

There are several ways to prevent HIV transmission. For example, people living with HIV can take antiretroviral medications daily to reduce viral load to undetectable levels. This practically eliminates any risk of transmitting HIV during sex.

When having sex, always use a condom or other barrier method. Partners without HIV can also look into taking pre-exposure prophylaxis (PrEP). People who inject drugs can use safe injection sites and needle exchange programs.

When HIV first emerged, living with HIV carried tremendous social stigma. Today, improving HIV education and banishing the myths about HIV transmission are the best ways to end the stigma that can be associated with living with HIV.

Read this article in Spanish.