HIV: what it is, how it spreads, testing and treatment

HIV (human immunodeficiency virus) is a virus that weakens the immune system. There is no cure, but it is very treatable: with antiretroviral treatment, people with HIV live long, healthy lives, and if their viral load is undetectable they cannot pass the virus on through sex.

What HIV is, and what AIDS is

HIV infects certain immune cells. Without treatment, it slowly destroys them over many years. AIDS is the advanced stage of untreated HIV, when the immune system is badly damaged. HIV and AIDS are not the same thing: with early diagnosis and treatment, most people with HIV never reach that stage.

HIV is still common. According to the World Health Organization (WHO), around 41 million people were living with HIV worldwide at the end of 2025, and about 1.2 million people acquired it that year.

Symptoms and when they appear

Many people notice nothing for years. Others get a flu-like illness 2 to 6 weeks after infection:

• fever and tiredness;
• a sore throat;
• swollen glands;
• aching muscles or a rash.

These symptoms last a few days and go away on their own. They are common in many other infections, so they cannot tell you whether you have HIV. Having no symptoms does not rule it out either. Only a test can.

How HIV is passed on, and how it is not

HIV is passed on through blood, semen, pre-cum, vaginal and rectal fluids, and breast milk. The main routes are:

• Anal or vaginal sex without a condom or PrEP with someone who has HIV and is not on treatment. Anal sex carries the highest risk (read more about safe anal sex).
• Oral sex: the risk is very low but not zero, and it rises if there are sores in the mouth or on the genitals.
• Sharing needles, syringes or other injecting equipment.
• During pregnancy, birth or breastfeeding, if the mother is not on treatment.

HIV is not passed on by hugging, kissing, saliva, tears or sweat. Nor by sharing cups, cutlery or toilets, or by mosquito bites. Everyday contact is safe.

Testing: when and how

An HIV test is simple and confidential. You can have a blood test at your GP surgery or a sexual health clinic, a rapid finger-prick test, or use a self-test kit.

What matters is the window period, the time before a test can pick up the infection:

• A laboratory blood test (antigen and antibody) can usually detect HIV 18 to 45 days after exposure.
• Rapid tests and self-tests, which look for antibodies, can take up to 90 days (about 3 months).

If your result is negative but you are still within the window period, test again later. A positive self-test always needs a confirmation test at a clinic. If you have different partners, regular testing is a good idea; here is how often to have an STI test.

Treatment: HIV can be controlled

HIV is treated with antiretroviral medicines. This is usually one tablet a day; long-acting injections are also an option for some people. Treatment does not remove the virus, but it stops it multiplying, protects the immune system and prevents transmission.

It is best to start as soon as possible, on the day of diagnosis or shortly after. The viral load usually becomes undetectable within a few months, often around six. Until your care team confirms it is undetectable, use condoms or other protection. With regular check-ups, life expectancy is close to that of the general population.

Pregnancy

A woman with HIV can have a pregnancy and a baby without HIV. If she starts or stays on treatment and has an undetectable viral load at birth, the risk of passing HIV on is very low. That is why an HIV test is part of routine antenatal screening. You will find more in our pregnancy and postpartum guide.

Prevention: condoms, PrEP and PEP

• Condoms protect against HIV and other STIs when used correctly from the start. Check the most common condom mistakes.
• PrEP (pre-exposure prophylaxis): medicine taken by people without HIV to avoid getting it. It is highly effective, and in the UK it is free through sexual health services.
• PEP (post-exposure prophylaxis): emergency treatment after a risky exposure. It must be started as soon as possible and always within 72 hours. Ask at a sexual health clinic or A&E.
• Treatment as prevention: when a person with HIV has an undetectable viral load, their treatment protects their partners.
• Not sharing injecting equipment.

When to get help

Go to a sexual health clinic or A&E the same day if you had a risky exposure in the last 72 hours: you may be offered PEP. Book a test if you have had sex without protection, have been diagnosed with another STI, or have a partner with HIV who is not on treatment. You can also ask about PrEP. Staff will see you without judgement.