How Is HIV Transmitted?
Reviewed by: HU Medical Review Board | Last reviewed: September 2019 | Last updated: February 2023
Although we may more commonly hear of HIV in certain populations or areas of the world, it’s important to remember that HIV can affect anyone. Although HIV may be more easily transmitted by certain sexual behaviors or among those injecting drugs, the virus has the ability to infect anyone, anywhere, as long as there is a transmission event.
A transmission event refers to HIV-containing fluids coming into contact with an opening in the skin (such as a wound) or the mucous membranes of an individual without the virus. Mucous membranes are the surfaces that line the inside of the mouth, penis, vagina, and rectum. Mucous membranes are also found in the eyes and nose.
What bodily fluids transmit HIV?
Bodily fluids that can contain and transmit the virus include:
- Rectal fluids
- Vaginal fluids
- Breast milk
- Pre-seminal fluid (also called precum)1
Even if an HIV-negative individual comes into contact with HIV-containing bodily fluids, it’s still not guaranteed that they will get the virus.
It has been estimated that 15 percent of HIV-positive individuals in the US, including 51 percent of HIV-positive 13-24 year olds, don’t know that they have the condition.2 This makes it possible for the virus to be transmitted amongst individuals who are unaware that transmission may be occurring. HIV does not discriminate based on age, race, location, socioeconomic status, or sexual orientation. It can transmit to anyone who is exposed. Additionally, just because a person has HIV, it does not mean they were engaging in risky sexual behaviors or drug use since there are several ways in which the virus can be transmitted.
Behaviors that increase risk
Although HIV can be transmitted through HIV-containing bodily fluids, there are some behaviors that might increase a person’s chance of getting the virus. The main methods of transmission in the United States include:
- Unprotected anal and vaginal sex: Having sex without a condom, especially with multiple sexual partners, can increase an individual’s risk of getting HIV. There are medications that can help prevent the transmission of HIV or to suppress the virus in an HIV-positive individual, however, having unprotected sex without these can also increase the risk of transmission. Unprotected anal sex has the highest risk, especially for the person receiving (also called bottoming). Unprotected vaginal sex is the next riskiest behavior.
- Sharing needles: Aside from unprotected sex, another high-risk behavior is needle sharing. As the opioid crisis continues in America, more individuals are using intravenous drugs, and potentially, practicing non-sterile techniques while doing so. Although HIV cannot live long outside the body, it does have the potential to live inside syringes or needles for several weeks.1,3-5
Another important factor that can increase an individual’s risk of getting or transmitting the virus is the presence of another sexually transmitted infection (STI). Individuals with STI’s including genital herpes, syphilis, chlamydia, and gonorrhea, among others, are three times more likely to get or transmit HIV. Essentially, the previous risk of any specific sexual behavior increases if there is another STI present during the act.4,6,7
This increase in risk can happen for a variety of reasons. First, some STIs, like herpes, lead to open sores on or around the genitals that can serve as areas for transmission. Even STIs that don’t commonly produce sores, like chlamydia, can still lead to an increased amount of inflammation and inflammatory cells in the body that can be transmitted by HIV. When some STIs that co-occur with HIV are left untreated, like herpes, the affected individual may have a higher viral load than another HIV-positive individual who does not have a co-occurring herpes transmission.4,7
Less common routes of transmission
In addition to sharing needles and unprotected anal or vaginal intercourse, there are other ways HIV can be transmitted. Several of these include:
- Mother-to-child transmission: If an HIV-positive woman is pregnant, it’s possible for her to transmit the virus to her baby, especially if she is not taking any medications to control her HIV. HIV transmission can occur during pregnancy, childbirth, or while breastfeeding, so many women will be tested for HIV when they become pregnant and started on treatment if they are HIV-positive.
- Accidental needle stick: Transmission after being stuck with an HIV-contaminated needle or other sharp object is mostly a concern for healthcare workers who may be working with HIV-positive patients. However, the risk of transmission through this route is much less than that of injection/intravenous drug use. Safety precautions, including retractable needles and special containers for the disposal of needles and other sharps, are rigorously practiced by healthcare settings in order to keep this transmission risk low.
- Oral sex: Oral sex, also called fellatio, blowjob, giving head (when involving the penis), cunnilingus, eating out (when involving the vagina), anilingus, or rimming (when involving the anus), involves using the mouth to stimulate a partner’s genitals. Although low, there is a small risk of transmitting HIV during this act. The risk increases when sores are present in the mouth or on the genitals of one of the partners, blood (including menstrual blood) is present, when a male partner ejaculates into their partner’s mouth, or when another STI is present.1,3-8
Factors that increase the risk of transmission during oral sex can also increase an individual’s risk of getting or transmitting the virus during deep, open-mouth kissing, including the presence of blood from bleeding gums or open sores. You cannot get HIV from closed-mouth kissing.1
Extremely rare cases of HIV transmission
Some methods of transmitting HIV are more theoretical in nature and have not actually been reported in the United States. One of these theoretical situations is when getting a tattoo or body piercing. Although this has not actually been seen, in theory, poorly sanitized equipment, especially needles, could possibly transmit HIV.4 This is why it’s important to visit a reputable and licensed tattoo artist or piercer when getting any new body art.
Before donated organs and blood were thoroughly monitored for the presence of HIV, it was possible to contract the virus after a blood transfusion or organ transplant. However, the current United States blood supply and all donated organs and tissues are very carefully monitored for HIV and other blood-borne diseases, so the risk of getting the virus from these procedures is incredibly low.1,3
Ways that HIV is not transmitted
As mentioned, the bodily fluids that can contain HIV include blood, semen, pre-seminal fluid (precum), vaginal fluid, rectal fluid, and breastmilk. HIV cannot be transmitted through:
- Casual contact (shaking hands, hugging, cuddling)
- Closed-mouth kissing
- Insects (including ticks and mosquitos)
- Toilet seats
- Food or drinks
- Donating blood1,4