Learn About HIV Prevention and Risk Reduction

Understanding HIV Transmission: How the Virus Spreads

HIV, or human immunodeficiency virus, is spread through specific bodily fluids and contact routes. Understanding exactly how transmission happens is one of the most important steps in prevention. The virus lives in blood, semen, vaginal fluid, rectal fluid, and breast milk. It does not survive in saliva, sweat, tears, or urine, which means everyday contact like hugging, kissing, or sharing food carries no transmission risk.

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HIV spreads primarily through three routes: sexual contact, blood exposure, and from mother to child. During sexual activity, the virus can enter the body through the lining of the vagina, vulva, penis, rectum, or mouth. The rectal lining is particularly susceptible because it is thin and contains many immune cells that HIV targets. The vaginal lining is also vulnerable, though slightly less so than the rectal tissue. Small tears in these tissues during sex create additional entry points for the virus.

Blood-to-blood contact represents another transmission route. This happens when people share injection equipment for drugs, including needles, syringes, cookers, and cotton. Healthcare workers may face occupational exposure through needlestick injuries, though this risk is less than 0.3 percent per incident. Transfusions of unscreened blood products can transmit HIV, but modern screening has made this extremely rare in developed countries.

Mother-to-child transmission, also called vertical transmission, can occur during pregnancy, delivery, or breastfeeding. However, with medical treatment, the risk drops dramatically. Women taking antiretroviral therapy with an undetectable viral load have virtually no risk of transmitting HIV to their baby during pregnancy and childbirth—a concept called U=U (undetectable equals untransmittable).

Important note: you cannot get HIV from touching someone with HIV, sharing clothing or bedding, donating blood, mosquito bites, or contact sports. The virus requires direct access to the bloodstream or mucous membranes, which everyday activities do not provide.

Practical takeaway: HIV requires specific conditions to transmit—direct contact between infected bodily fluids and either blood or mucous membranes. Knowing these specific routes helps you understand which prevention methods work and why.

Sexual Transmission Prevention: Barrier Methods and Beyond

Condoms remain one of the most effective tools for preventing HIV during sexual activity. Male condoms, typically made from latex or polyurethane, create a barrier between partners and prevent exchange of sexual fluids. When used consistently and correctly, condoms reduce the risk of HIV transmission by approximately 95 percent. "Consistent" means using one every single time; even occasional unprotected sex significantly increases risk. "Correct" means putting it on before any sexual contact, ensuring proper fit, and using water-based or silicone-based lubricant rather than oil-based products that degrade latex.

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Female condoms offer another option. These pouches line the vagina or rectum and are made from nitrile, a non-latex material. They are less commonly used than male condoms but provide similar protection when used correctly. Both types prevent pregnancy as well as HIV transmission.

For people at higher risk of HIV through receptive anal or vaginal sex, a medication called PrEP (pre-exposure prophylaxis) offers significant protection. PrEP involves taking antiretroviral medications daily, even when not having sex. Studies show that PrEP reduces the risk of sexually acquired HIV by more than 90 percent in people who take it consistently. The two main medications are Truvada and Descovy, both taken as a daily pill, though longer-acting injection options are emerging. PrEP works by building up medication levels in the bloodstream and genital tissues, creating a protective barrier against infection.

Another preventive option is PEP (post-exposure prophylaxis), which is medication taken after potential exposure to HIV. PEP must start within 72 hours of exposure—ideally within 2 hours—and continues for 28 days. It is about 81 percent effective at preventing infection when started promptly and taken consistently. PEP is intended for emergencies like condom breakage, sexual assault, or needlestick injury, not as a regular prevention method.

For serodiscordant couples (where one partner has HIV and one does not), U=U changes prevention approaches. An HIV-positive partner with an undetectable viral load—meaning the virus level in blood is so low it cannot be measured or transmitted—poses no transmission risk during sex. This means condoms are not required for transmission prevention, though they may still be used for other reasons and to prevent other sexually transmitted infections.

Practical takeaway: Multiple prevention options exist for different situations and preferences. Combining methods—such as condoms plus PrEP—provides even greater protection than either method alone.

Reducing Risk Through Testing and Knowing Your Status

Regular HIV testing is a cornerstone of prevention because it identifies infection early, when treatment is most effective, and prevents unknowing transmission to partners. The CDC recommends that everyone aged 13 to 64 receive at least one HIV test as part of routine healthcare. People with behaviors that increase risk—such as multiple partners, inconsistent condom use, or injection drug use—should test more frequently, ideally every three to six months.

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Several types of HIV tests exist, each with different detection windows. The detection window is the time between infection and when a test can reliably detect the virus. Antibody tests, which look for proteins the immune system makes in response to HIV, typically detect infection 18 to 45 days after exposure. Antigen/antibody tests, which detect both HIV antibodies and the p24 antigen protein, can detect infection as early as 18 to 45 days. Nucleic acid tests (NAT), which look for HIV genetic material directly, are the fastest, detecting infection as soon as 10 to 33 days after exposure. NAT tests are most sensitive but also most expensive and are typically used for screening blood donations or confirming positive results.

Testing locations vary. Doctor's offices and hospitals offer tests as part of regular care. Many public health departments and community health centers offer free or low-cost testing with no insurance required. Rapid tests available in some clinics provide results within 20 minutes. At-home tests, which involve a finger prick to collect blood or an oral swab, are available over-the-counter and provide results in 15 to 60 minutes. Home tests have accuracy rates of 99.1 percent for positive results, though false negatives are more possible, so a negative result during the window period may require follow-up testing.

Knowing your status empowers you to take action. If you test positive, starting antiretroviral treatment promptly offers tremendous benefits: you can live a long, healthy life and reach an undetectable viral load, meaning you cannot transmit HIV through sex (U=U). If you test negative and have ongoing risk factors, you might explore PrEP. If you tested during the window period and had a recent exposure, follow-up testing a few weeks later confirms your status.

Testing also helps identify other sexually transmitted infections (STIs) like chlamydia, gonorrhea, syphilis, and hepatitis B. Many STIs increase HIV transmission risk, so identifying and treating them reduces your overall risk. Some locations offer comprehensive screening that tests for multiple infections simultaneously.

Practical takeaway: Regular testing identifies your status so you can make informed decisions about prevention methods. Testing frequency depends on your risk level—from once yearly for people with lower risk to every three to six months for those with higher risk.

Injection Drug Use: Preventing HIV in the Context of Substance Use

People who inject drugs face elevated HIV risk because of shared equipment. When multiple people use the same needle, syringe, cooker, cotton, or rinse water, traces of blood from one person can enter another's bloodstream. In the United States, about 4 percent of new HIV diagnoses occur among people who inject drugs. However, prevention strategies are highly effective in this population.

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Needle and syringe programs (NSPs) provide sterile injection equipment at no cost, eliminating the primary transmission route. These programs distribute new needles and syringes, cookers, cotton filters, alcohol pads, and rinse water. People can return used equipment for proper disposal. Research shows that NSPs reduce HIV transmission risk by approximately 50