HIV is transmitted when certain body fluids from a person with HIV — blood, semen, vaginal fluid, rectal fluid, or breast milk — enter another person's bloodstream or mucous membranes. The most common routes are condomless anal or vaginal sex and sharing needles. It is not spread by casual contact, saliva, or kissing.
How is HIV transmitted?
HIV (human immunodeficiency virus) can only spread through a limited set of body fluids. According to the CDC, these are blood, semen, pre-seminal fluid, rectal fluid, vaginal fluid, and breast milk. For transmission to happen, one of these fluids must reach a mucous membrane (found inside the rectum, vagina, penis tip, and mouth), enter through damaged tissue, or be injected directly into the bloodstream.
The most common ways this occurs are:
- Condomless anal or vaginal sex with a partner who has HIV and a detectable viral load. Receptive anal sex carries the highest per-act risk.
- Sharing needles, syringes, or other drug-injection equipment.
- From parent to child during pregnancy, childbirth, or breastfeeding — though this is now rare with treatment.
Having another untreated STI can raise the risk of acquiring HIV, which is one reason routine STI testing matters.
What does not transmit HIV
The virus does not survive long outside the body and cannot reproduce outside a human host. You cannot get HIV from:
- Saliva, tears, or sweat
- Closed-mouth kissing, hugging, or shaking hands
- Sharing food, dishes, or toilets
- Insect or mosquito bites
- Touching surfaces or everyday objects
Recognizing the signs
Many people have no symptoms for years. When early symptoms do appear, the NHS describes a short, flu-like illness roughly 2–6 weeks after exposure, sometimes including:
- A high temperature or fever
- A sore throat
- A skin rash
- Swollen glands
- Muscle aches and tiredness
Because these signs are easy to miss or mistake for something else — and because they can overlap with other infections — symptoms alone are never a reliable guide. Read more about timing in How Long Do STIs Take to Show Up?. The only way to know your status is to test.
Testing for HIV
HIV testing is fast, confidential, and widely available. Most tests use a blood sample, while some clinics offer a rapid finger-prick or saliva test with same-day results. Self-test kits are also an option in many regions.
The window period
After exposure, the body needs time to produce enough antibodies or viral markers to be detected. The CDC explains that no test can detect HIV immediately, and that antibody tests can usually detect HIV 23 to 90 days after exposure, while newer antigen/antibody and nucleic-acid tests can detect it sooner. A negative test taken too early may need to be repeated after the window period for that test closes.
A positive screening result always requires confirmatory testing by a trained health worker, as the WHO emphasizes. A clear, step-by-step overview of the process is in our STI Testing guide.
Preventing HIV
There is no vaccine, but several highly effective tools exist. The CDC and WHO recommend combining them:
- Condoms. Used correctly and consistently, condoms are highly effective at preventing HIV and many other STIs.
- PrEP (pre-exposure prophylaxis). Medicine taken by HIV-negative people that is highly effective at preventing HIV when taken as prescribed. It now comes as daily pills and, in some places, long-acting injections.
- PEP (post-exposure prophylaxis). Emergency medicine started within 72 hours of a possible exposure. Sooner is better — contact a clinic or emergency service urgently.
- Treatment as prevention (U=U). A person with HIV who takes treatment and maintains an undetectable viral load cannot transmit HIV sexually.
- Never sharing needles or injection equipment.
For a broader, evidence-based checklist, see How to Prevent STIs, and explore related topics on our STIs & Testing hub.
Living with HIV
HIV is no longer the diagnosis it once was. With antiretroviral therapy (ART) — usually a single tablet once a day — most people with HIV live long, healthy lives and never develop AIDS. The WHO and NHS both confirm that early diagnosis and consistent treatment lead to a normal lifespan and, through U=U, protect partners too. Ongoing care and monitoring with a provider are essential to keep the virus suppressed.
The bottom line
HIV is transmitted only through specific body fluids reaching a mucous membrane, broken skin, or the bloodstream — most often via condomless sex or shared needles, never through everyday contact like kissing or sharing food. Testing is the only way to know your status, and powerful prevention tools exist: condoms, PrEP, PEP, and treatment that makes the virus untransmittable. If you are unsure about your risk, testing options, or whether PrEP or PEP is right for you, speak with a qualified healthcare provider. This article is general education and is not a substitute for individualized medical advice.
