Overview
HIV (Human Immunodeficiency Virus) attacks and weakens the immune system by destroying CD4 cells (T-helper lymphocytes). Without treatment, the immune system is gradually destroyed, leading to AIDS (Acquired Immunodeficiency Syndrome), where the body cannot fight infections or cancers. With modern antiretroviral therapy, HIV is a manageable chronic condition and life expectancy is near-normal.
How common is it?
UNAIDS estimated that 40.8 million people were living with HIV worldwide in 2024. Some people do not know they have HIV, so testing matters even without symptoms.
Causes and risk factors
HIV is transmitted through specific body fluids: blood, semen, vaginal fluids, rectal fluids, and breast milk. It is not spread through everyday contact such as hugging, sharing food, or insect bites.
Common risk factors
- Anal or vaginal sex without effective prevention when a partner has transmissible HIV; sustained undetectable viral load on effective treatment prevents sexual transmission
- Sharing injecting drug equipment
- Mother to child transmission during birth or breastfeeding
- Blood transfusion with infected blood (rare in UK with screening)
- Needlestick injury with contaminated blood (healthcare workers)
Symptoms
- Many people have no symptoms for years after initial infection
- Acute HIV infection (2 to 4 weeks after exposure): flu-like illness with fever, rash, sore throat, swollen lymph nodes
- Without treatment: weight loss, night sweats, recurrent infections, thrush
- AIDS-defining illnesses: Pneumocystis pneumonia, toxoplasmosis, CMV retinitis, Kaposi sarcoma
When to see a doctor
If you may have been exposed to HIV within the last 72 hours, seek urgent assessment at a sexual health clinic or emergency department for post-exposure prophylaxis (PEP). Do not wait for symptoms or a home-test result. If the exposure was earlier, arrange testing and advice about when repeat testing is needed. Effective prevention and treatment are available.
Diagnosis
HIV tests look for antibodies, antigen or the virus itself, depending on the test. Each has a window period, so an early negative result may need repeating at the time advised by the clinic. Do not wait for a test before seeking urgent PEP assessment after possible recent exposure. Viral load and CD4 count guide ongoing HIV care.
Treatments
Antiretroviral therapy (ART)
Daily oral tablets combining 2 to 3 different antiretroviral drugs suppress viral replication to undetectable levels. People with undetectable viral load cannot transmit HIV to sexual partners (U=U: Undetectable = Untransmittable).
PrEP (Pre-Exposure Prophylaxis)
PrEP prevents HIV in people who do not have HIV; it does not treat established infection. A clinic chooses a suitable regimen and arranges HIV, kidney and hepatitis B checks as needed. On-demand tablets are not suitable for every exposure or for people with hepatitis B. Follow the clinic's instructions rather than adapting a schedule yourself.
PEP (Post-Exposure Prophylaxis)
PEP is emergency treatment after a possible exposure. Seek assessment as soon as possible: it must be started within 72 hours, and earlier is better. A prescribed course usually lasts 28 days, with follow-up testing. Do not wait for symptoms or a home-test result.
Self-care and lifestyle
- Adhere strictly to ART medication as missing doses allows viral rebound
- Regular sexual health screenings and STI treatment reduce complications
- Inform sexual partners of your HIV status and use condoms to prevent other STIs
- Live a healthy lifestyle: exercise, healthy diet, and avoid smoking which worsens immunosuppression
Prevention
Condom use during sex, PrEP for high-risk individuals, clean needle programmes, HIV testing, and treatment (treatment as prevention) are all evidence-based prevention strategies.
Sources for targeted updates
Updated: 24 October 2026. Targeted corrections to frequency, risk factors, diagnosis, treatment, key facts. This update covers the named sections; a full review of the remaining guide is pending.