Introduction 

HIV is a virus that attacks the immune system, and weakens your ability to fight infections and disease. It's most commonly caught by having sex without a condom.

It can also be passed on by sharing infected needles and other injecting equipment, and from an HIV-positive mother to her child during pregnancy, birth and breastfeeding.

HIV stands for human immunodeficiency virus. The virus attacks the immune system, and weakens your ability to fight infections and disease.

There is no cure for HIV, but there are treatments to enable most people with the virus to live a long and healthy life.

AIDS is the final stage of HIV infection, when your body can no longer fight life-threatening infections. With early diagnosis and effective treatment, most people with HIV will not go on to develop AIDS.

How do you get HIV?

HIV is found in the body fluids of an infected person, which includes semen, vaginal and anal fluids, blood, and breast milk. It is a fragile virus and does not survive outside the body for long.

HIV cannot be transmitted through sweat or urine.

The most common way of getting HIV in the UK is by anal or vaginal sex without a condom. According to statistics from Public Health England, 95% of those diagnosed with HIV in the UK in 2013 acquired HIV as a result of sexual contact.

Other ways of getting HIV include:

  • using a contaminated needle, syringe or other injecting equipment
  • transmission from mother to baby during pregnancy, birth or breastfeeding

It's also possible for HIV to spread through oral sex and sharing sex toys, although the chances of this happening are very low. For example, it's estimated that you only have a 1 in 5,000 chance of getting HIV if you give unprotected oral sex to someone with the infection.

Read more about what causes HIV.

Getting tested for HIV

Seek medical advice as soon as possible if you think you might have been exposed to HIV.

The only way to find out if you have HIV is to have an HIV test. This involves testing a sample of your blood or saliva for signs of the infection.

It's important to be aware that:

  • emergency anti-HIV medication called PEP (post-exposure prophylaxis) may stop you becoming infected if started within three days of possible exposure to the virus, and starting it as soon as possible is recommended
  • an early diagnosis means you can start treatment sooner, which can improve your chances of controlling the condition
  • HIV tests may need to be repeated one to three months after potential exposure to HIV infection (this is known as the "window period"), but you shouldn't wait this long to seek help
  • you can get tested in a number of places, including your GP surgery, sexual health clinics and clinics run by charities such as the find HIV testing services near you 
  • clinic tests can sometimes give you a result in minutes, although it may take a few days to get the result of a more detailed blood test
  • home-testing or home-sampling kits are available to buy or order online or from pharmacies – depending on the type of test you use, your result will be available in a few minutes or a few days

If your first test suggests you have HIV, a further blood test will need to be carried out to confirm the result. If this is positive, you'll be referred to a specialist HIV clinic for some more tests and a discussion about your treatment options.

Read more about diagnosing HIV.

Treating and living with HIV

Although there is no cure for HIV, treatments are now very effective, enabling people with HIV to live long and healthy lives.

Medication, known as antiretrovirals, work by stopping the virus replicating in the body, allowing the immune system to repair itself and preventing further damage. These medicines come in the form of tablets, which need to be taken every day.

HIV is able to develop resistance to a single HIV drug very easily, but taking a combination of different drugs makes this much less likely. Most people with HIV take a combination of three antiretrovirals and it is vital that the medications are taken every day as recommended by your doctor.

For people living with HIV, taking effective antiretroviral therapy (where the HIV virus is "undetectable" in blood tests) will significantly reduce the risk of passing on HIV to sexual partners. It is rare for a pregnant woman living with HIV to transmit it to their babies, provided they receive timely and effective antiretroviral therapy and medical care.

You will also be encouraged to take regular exercise, eat a healthy diet, stop smoking and have yearly flu jabs to minimise the risk of getting serious illnesses.

Without treatment, the immune system will become severely damaged and life-threatening illnesses such as cancer and severe infections can occur. This is known as late-stage HIV infection or AIDS.

Read more about living with HIV.

Preventing HIV

Anyone who has sex without a condom or shares needles is at risk of HIV infection.

The best way to prevent HIV is to use a condom for sex and to never share needles or other injecting equipment (including syringes, spoons and swabs). Knowing your HIV status and that of your partner is also important.

For people with HIV, effective antiretroviral therapy significantly reduces the risk of passing HIV to sexual partners.

How common is HIV?

At the end of 2014, there were an estimated 103,700 people in the UK living with HIV. The majority were infected through sex (43,000 gay and bisexual men and 54,100 heterosexuals).

An estimated 17% of people with HIV (18,100) do not know they are infected.

Around one in every 360 people in the UK has HIV, but the two groups with highest rates of HIV are gay and bisexual men (approximately 1 in 20) and Black African heterosexuals (approximately 1 in 56 men and 1 in 22 women).

The World Health Organization estimates that around 35 million people in the world are living with HIV. The virus is more common in many sub-Saharan African countries.

Find out more about:



HIV vaccine trials

Two clinical trials are recruiting HIV negative healthy volunteers at Imperial College London. For information about the trials please email hivvaccinetrial@imperial.ac.uk or phone 0800 358 3001.

If you take part you will need to attend the centre regularly for the next six to 12 months and will be reimbursed for your time.

For details of UK trials currently recruiting, follow the Help Make History campaign @HelpMakeIt_MRC on Twitter.

Page last reviewed: 08/09/2014

Next review due: 08/09/2016