HIV 101




HIV is spread from person to person through certain body fluids if one of the people already has HIV.

These bodily fluids are:

  • Blood

  • Semen (cum)

  • Pre-seminal fluid (pre-cum)

  • Rectal fluids

  • Vaginal fluids

  • Breast milk

These body fluids must come into contact with a mucous membrane or damaged tissue or be directly injected into your bloodstream (by a needle or syringe) for transmission to possibly occur. Mucous membranes are the soft, moist areas just inside the openings to your body. They can be found inside the rectum, the vagina or the opening of the penis, and the mouth.



HIV is spread mainly by having sex with someone who has HIV.

  • In general:

    • Anal sex (penis in the anus of a man or woman) is the highest-risk sexual behavior. Receptive anal sex (“bottoming”) is riskier than insertive anal sex (“topping”).

    • Vaginal sex (penis in the vagina) is the second highest-risk sexual behavior.

    • Having multiple sex partners or having sexually transmitted infections can increase the risk of HIV infection through sex. Sharing needles, syringes, rinse water, or other equipment (“works”) used to prepare injection drugs with someone who has HIV.


Less commonly, HIV may also be spread by:

  • Being born to an infected mother. HIV can be passed from mother to child during pregnancy, birth, or breastfeeding.

  • Being stuck with an HIV-contaminated needle or other sharp object. This is a risk mainly for health care workers.

  • Receiving blood transfusions, blood products, or organ/tissue transplants that are contaminated with HIV. This risk is extremely small because of rigorous testing of the US blood supply and donated organs and tissues.

  • Eating food that has been pre-chewed by an HIV-infected person. The contamination occurs when infected blood from a caregiver’s mouth mixes with food while chewing, and is very rare.

  • Oral sex—using the mouth to stimulate the penis, vagina, or anus (fellatio, cunnilingus, and rimming). Giving fellatio (mouth to penis oral sex) and having the person ejaculate (cum) in your mouth is riskier than other types of oral sex.

  • Deep, open-mouth kissing if the person with HIV has sores or bleeding gums and blood is exchanged. HIV is not spread through saliva. Transmission through kissing alone is extremely rare.


HIV is NOT spread by:

  • Air or water

  • Insects, including mosquitoes or ticks

  • Saliva, tears, or sweat

  • Casual contact, like shaking hands, hugging or sharing dishes/drinking glasses

  • Drinking fountains

  • Toilet seats


HIV is not spread through the air and it does not live long outside the human body.


Having an undetectable viral load greatly lowers the chance that a person living with HIV can transmit the virus to a partner, but there is still some risk. “Viral load” refers to the amount of HIV in an infected person’s blood. An “undetectable viral load” is when the amount of HIV in a person’s blood is so low that it can’t be measured. Antiretroviral therapy (ART) reduces a person’s viral load, ideally to an undetectable level, when taken consistently and correctly. However, a person with HIV can still potentially transmit HIV to a partner even if they have an undetectable viral load, because:

  • HIV may still be found in a person’s genital fluids (e.g., semen, vaginal fluids). The viral load test only measures virus in a person’s blood.

  • A person’s viral load may go up between tests. When this happens, they may be more likely to transmit HIV to partners.

  • Sexually transmitted diseases (STDs) increase viral load in a person’s genital fluids.


For more information on how HIV is spread, see HIV Transmission Basics.



The terms “HIV” and “AIDS” can be confusing because both terms refer to the same disease. However, “HIV” refers to the virus itself, and “AIDS” refers to the late stage of HIV infection, when an HIV-infected person’s immune system is severely damaged and has difficulty fighting diseases and certain cancers. Before the development of certain medications, people with HIV could progress to AIDS in just a few years. But today, most people who are HIV-positive do not progress to AIDS because if you have HIV and you take antiretroviral therapy (ART) consistently, you can keep the level of HIV in your body low. This will help keep your body strong and healthy and reduce the likelihood that you will ever progress to AIDS. It will also help lower your risk of transmitting HIV to others.


For more information about the difference between HIV and AIDS, see What is HIV/AIDS?



The only way to know for sure if you have HIV is to get tested. Testing is relatively simple. You can get an HIV test from your doctor or healthcare provider, community health center, Veteran’s health center, Title X family planning clinic, and other locations. There also are FDA-approved HIV home test kits you can use.


For an HIV testing station near you, go to AIDS locator.