HIV, or human immunodeficiency virus, attacks the immune system. Without treatment, HIV can progress to AIDS, the most advanced stage of infection. Modern antiretroviral therapy can control the virus, protect the immune system and allow people with HIV to live long, healthy lives.
How HIV Spreads
HIV can be transmitted through certain body fluids, including blood, semen, pre-seminal fluid, rectal fluids and vaginal fluids. Transmission most commonly occurs through anal or vaginal sex or through sharing needles, syringes or other injection equipment. HIV can also be transmitted during pregnancy, childbirth or breastfeeding.
HIV is not spread through ordinary social contact such as hugging, sharing food, toilets or insect bites.
Symptoms and Testing
Some people develop flu-like symptoms within several weeks of infection, while others have no noticeable early symptoms. Symptoms alone cannot diagnose HIV. The only way to know your HIV status is to be tested.
Different HIV tests have different window periods. If testing is performed soon after a possible exposure, repeat testing may be needed. A reactive or positive screening test requires follow-up testing to confirm the diagnosis.
Prevention
HIV prevention options include condoms, avoiding shared injection equipment, pre-exposure prophylaxis (PrEP) for people who may benefit from ongoing protection, and post-exposure prophylaxis (PEP) after a possible exposure. PEP should be started as soon as possible and must be started within 72 hours of exposure.
Treatment and U=U
Antiretroviral therapy (ART) is recommended as soon as possible after an HIV diagnosis. Treatment reduces the amount of virus in the blood, known as the viral load. When treatment reduces HIV to an undetectable level and that level is maintained, the person will not transmit HIV to sexual partners. This is known as Undetectable = Untransmittable, or U=U.
HIV treatment does not prevent other sexually transmitted infections, so additional prevention and appropriate STI testing may still be important.
When to Seek Medical Care
Seek medical advice promptly after a possible HIV exposure so that PEP can be considered within the required time window. People with diagnosed HIV should remain connected to regular medical care and take treatment as prescribed.
Seek urgent medical assessment for severe breathing difficulty, confusion, new neurological symptoms, persistent high fever or rapidly worsening illness.
Related Topics
Sources and Further Reading
- Centers for Disease Control and Prevention: About HIV
- Centers for Disease Control and Prevention: HIV Testing
- World Health Organization: HIV and AIDS
Last reviewed: 4 September 2026. This information does not replace individual medical assessment or treatment.