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Basic Questions and Answers About HIV Transmission

September 6, 2016

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Myths persist about how HIV is transmitted. This section provides the facts about HIV risk from different types of sex, injection drug use, and other activities.

Table of Contents


How Is HIV Passed From One Person to Another?

You can get or transmit HIV only through specific activities. Most commonly, people get or transmit HIV through sexual behaviors and needle or syringe use.

Only certain body fluids -- blood, semen (cum), pre-seminal fluid (pre-cum), rectal fluids, vaginal fluids, and breast milk -- from a person who has HIV 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 occur. Mucous membranes are found inside the rectum, vagina, penis, and mouth.

In the United States, HIV is spread mainly by

  • Having anal or vaginal sex with someone who has HIV without using a condom or taking medicines to prevent or treat HIV.
    • Anal sex is the highest-risk sexual behavior. For the HIV-negative partner, receptive anal sex (bottoming) is riskier than insertive anal sex (topping).
    • Vaginal sex is the second-highest-risk sexual behavior.
  • Sharing needles or syringes, rinse water, or other equipment (works) used to prepare drugs for injection with someone who has HIV. HIV can live in a used needle up to 42 days depending on temperature and other factors.

Less commonly, HIV may be spread

  • From mother to child during pregnancy, birth, or breastfeeding. Although the risk can be high if a mother is living with HIV and not taking medicine, recommendations to test all pregnant women for HIV and start HIV treatment immediately have lowered the number of babies who are born with HIV.
  • By being stuck with an HIV-contaminated needle or other sharp object. This is a risk mainly for health care workers.

In extremely rare cases, HIV has been transmitted by

  • Oral sex -- putting the mouth on the penis (fellatio), vagina (cunnilingus), or anus (rimming). In general, there's little to no risk of getting HIV from oral sex. But transmission of HIV, though extremely rare, is theoretically possible if an HIV-positive man ejaculates in his partner's mouth during oral sex. To learn more about how to lower your risk, see Oral Sex and HIV Risk.
  • Receiving blood transfusions, blood products, or organ/tissue transplants that are contaminated with HIV. This was more common in the early years of HIV, but now the 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. The only known cases are among infants.
  • 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.
  • Contact between broken skin, wounds, or mucous membranes and HIV-infected blood or blood-contaminated body fluids.
  • Deep, open-mouth kissing if both partners have sores or bleeding gums and blood from the HIV-positive partner gets into the bloodstream of the HIV-negative partner. HIV is not spread through saliva.

Learn more about how to protect yourself and get information tailored to meet your needs from CDC's HIV Risk Reduction Tool (BETA).


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How Well Does HIV Survive Outside the Body?

HIV does not survive long outside the human body (such as on surfaces), and it cannot reproduce outside a human host. It is not spread by

  • Mosquitoes, ticks, or other insects.
  • Saliva, tears, or sweat that is not mixed with the blood of an HIV-positive person.
  • Hugging, shaking hands, sharing toilets, sharing dishes, or closed-mouth or "social" kissing with someone who is HIV-positive.
  • Other sexual activities that don't involve the exchange of body fluids (for example, touching).

Learn more about how to protect yourself and get information tailored to meet your needs from CDC's HIV Risk Reduction Tool (BETA).


Can I Get HIV From Anal Sex?

Yes. In fact, anal sex is the riskiest type of sex for getting or transmitting HIV.

HIV can be found in certain body fluids -- blood, semen (cum), pre-seminal fluid (pre-cum), or rectal fluids -- of a person who has HIV. Although receptive anal sex (bottoming) is much riskier for getting HIV than insertive anal sex (topping), it's possible for either partner -- the top or the bottom -- to get HIV. The bottom's risk is very high because the lining of the rectum is thin and may allow HIV to enter the body during anal sex. The top is also at risk because HIV can enter the body through the opening at the tip of the penis (or urethra); the foreskin if the penis isn't circumcised; or small cuts, scratches, or open sores anywhere on the penis. See the Prevention Q&As for information on how to lower your risk of getting HIV from anal sex.

Learn more about how to protect yourself and get information tailored to meet your needs from CDC's HIV Risk Reduction Tool (BETA).


Can I Get HIV From Vaginal Sex?

Yes. Vaginal sex is the sexual behavior with the second-highest risk for getting or transmitting HIV.

It is possible for either partner to get HIV from vaginal sex.

When a woman has vaginal sex with a partner who's HIV-positive, HIV can enter her body through the mucous membranes that line the vagina and cervix. Most women who get HIV get it from vaginal sex.

Men can also get HIV from having vaginal sex with a woman who's HIV-positive. This is because vaginal fluid and blood can carry HIV. Men get HIV through the opening at the tip of the penis (or urethra); the foreskin if they're not circumcised; or small cuts, scratches, or open sores anywhere on the penis. See the Prevention Q&As for information on how to lower your risk of getting HIV from vaginal sex.

Learn more about how to protect yourself and get information tailored to meet your needs from CDC's HIV Risk Reduction Tool (BETA).

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This article was provided by U.S. Centers for Disease Control and Prevention. Visit the CDC's website to find out more about their activities, publications and services.
 

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