Basic Questions and Answers About HIV Transmission
January 16, 2015
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.
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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), rectal fluids, 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 spread mainly by
Less commonly, HIV may be spread by
HIV does not survive long outside the human body (such as on surfaces), and it cannot reproduce. It is not spread by
Yes. In fact, having anal sex is the riskiest type of sex for getting or spreading HIV.
HIV can be found in the blood, semen (cum), preseminal fluid (pre-cum), or rectal fluid of a person infected with the virus. The bottom is at greater risk of getting HIV because the lining of the rectum is thin and may allow HIV to enter the body during anal sex, but the top is also at risk because HIV can enter through the opening of the penis or through small cuts, abrasions, or open sores on the penis. See the Prevention Q&As for more information.
Yes. In general vaginal sex is not as risky anal sex, but is still a high-risk behavior for HIV infection.
It is possible for either partner to become infected this way. This risk depends on many factors, including whether the partners are using condoms, whether the partner with HIV is using antiretroviral therapy (ART) consistently and correctly and whether the partner who is HIV-negative is using pre-exposure prophylaxis (PrEP) consistently and correctly. Condoms and HIV medicines can greatly lower the risk of transmitting HIV.
In women, HIV can be directly absorbed through the mucous membranes that line the vagina and cervix. The lining of the vagina can also sometimes tear and possibly allow HIV to enter the body.
In men, HIV can enter the body through the urethra (the opening at the tip of the penis) or through small cuts or open sores on the penis. Men who are not circumcised are at greater risk of HIV infection through vaginal sex than are circumcised men.
Risk for HIV infection increases if you or a partner also has a sexually transmitted disease (STD). See also Is there a connection between HIV and other sexually transmitted infections?
Many barrier methods that women use to prevent pregnancy (e.g., diaphragm, cervical cap) do not protect them against HIV or other STDs because they still allow infected semen (cum) to come in contact with the lining of the vagina.
Oral or hormonal contraceptives (e.g., birth control pills) do not protect women against HIV or other STDs.
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.