Overview
Acquired immunodeficiency syndrome, commonly abbreviated AIDS, is the advanced clinical condition that can develop in people infected with the human immunodeficiency virus (HIV). AIDS is not a separate virus but a syndrome — a set of signs, symptoms and infections resulting from severe damage to the immune system caused by HIV. For a concise clinical definition and resources see detailed definition.
Cause and biology
HIV is a virus that primarily attacks immune cells responsible for coordinating the body's defense against infections. Over time, if untreated, HIV reduces immune function and allows diseases that rarely cause severe illness in people with healthy immunity to become life‑threatening. The virus replicates within host cells and evades immune responses, a process described in virology sources such as virus reference.
Transmission and prevention
HIV spreads when blood, semen, vaginal fluids or breast milk from an infected person enter another person's bloodstream or mucous membranes. Common transmission routes include unprotected sexual contact, sharing injection equipment, and vertical transmission from mother to child during pregnancy, birth, or breastfeeding. Prevention strategies include consistent condom use, sterile needle programs, antiretroviral medicines for prevention (PrEP and PEP), and measures to prevent mother‑to‑child transmission; authoritative prevention guidance is available at prevention resources.
Signs, diagnosis and staging
People living with untreated HIV may remain asymptomatic for years before developing symptoms. As immune function declines, they become susceptible to opportunistic infections and certain cancers. Diagnosis relies on tests that detect HIV antibodies, antigens or viral genetic material; clinicians monitor immune status with laboratory markers and evaluate for clinical conditions that indicate progression to AIDS.
Treatment and prognosis
There is no cure for HIV infection, but antiretroviral therapy (ART) can suppress viral replication, preserve immune function, and prevent or reverse many complications. With sustained ART, many people with HIV live long, healthy lives and never develop the syndrome. Early diagnosis and adherence to treatment are key to improving outcomes.
History and public health
AIDS first came to international attention in the early 1980s and prompted global public‑health responses, research, and activism. Advances in diagnosis, treatment and prevention have transformed the condition from an often‑fatal illness into a chronic, manageable disease in many parts of the world. Nonetheless, social stigma, unequal access to care, and ongoing transmission remain major challenges.
Distinctions and notable facts
Important distinctions: HIV is the virus; AIDS is the clinical syndrome that can develop when HIV severely damages the immune system. Not everyone with HIV will progress to AIDS, especially when effective treatment is started early. Public health efforts emphasize testing, counseling, preventive measures and universal access to treatment to reduce illness and transmission.