In the United States, HIV is spread mainly by having sex or sharing injection drug equipment such as needles with someone who has HIV.

Only certain fluids—blood, semen (cum), pre-seminal fluid (pre-cum), vaginal fluids, and breast milk—from an HIV-infected person can transmit HIV. These fluids must come in contact with a mucous membrane or damaged tissue or be directly injected into the bloodstream (from a needle or syringe) for transmission to possibly occur. Mucous membranes can be found inside the rectum, the vagina, the opening of the penis, and the mouth.

In the United States, HIV is contracted mainly by:

  • Having sex with someone who has HIV:
    • Anal sex is the highest-risk sexual behavior. Receptive anal sex (bottoming) is riskier than insertive anal sex (topping).
    • Vaginal sex is the second most risky sexual behavior.
    • Having multiple sex partners or having other sexually transmitted infections can increase the risk of becoming infected through sex.
  • Sharing needles, syringes, rinse water, or other equipment (works) used with injection drugs with someone who has HIV.

Less commonly, HIV may be contracted 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.
  • Being bitten by a person with HIV. Each of the very small number of documented cases has involved severe trauma with extensive tissue damage and the presence of blood. There is no risk of transmission if the skin is not broken.
  • 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.
  • Contact between broken skin, wounds, or mucous membranes and HIV-infected blood or blood-contaminated body fluids. These reports have also been extremely rare.
  • 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.

Source: CDC