HIV (human immunodeficiency virus) is a virus that damages the cells in your immune system and weakens your ability to fight everyday infections and disease.

AIDS (acquired immune deficiency syndrome) is the name used to describe a number of potentially life-threatening infections and illnesses that happen when your immune system has been severely damaged by the HIV virus.

While AIDS cannot be transmitted from 1 person to another, the HIV virus can.

There's currently no cure for HIV, but there are very effective drug treatments that enable most people with the virus to live a long and healthy life. 

With an early diagnosis and effective treatments, most people with HIV will not develop any AIDS-related illnesses and will live a near-normal lifespan.

Most people experience a short flu-like illness 2 to 6 weeks after HIV infection, which lasts for a week or 2.

After these symptoms disappear, HIV may not cause any symptoms for many years, although the virus continues to damage your immune system.

This means many people with HIV do not know they're infected.

Anyone who thinks they could have HIV should get tested.

Some people are advised to have regular tests as they're at particularly high risk.

Read more about who's most at risk of HIV

HIV is found in the body fluids of an infected person. This includes semen, vaginal and anal fluids, blood and breast milk.

It's a fragile virus and does not survive outside the body for long.

HIV cannot be transmitted through sweat, urine or saliva.

The most common way of getting HIV in the UK is through having anal or vaginal sex without a condom.

Other ways of getting HIV include:

• sharing needles, syringes or other injecting equipment
• transmission from mother to baby during pregnancy, birth or breastfeeding

The chance of getting HIV through oral sex is very low and will be dependent on many things, such as whether you receive or give oral sex and the oral hygiene of the person giving the oral sex.

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

You can get tested in a number of places, including at a GP surgery, sexual health clinics and clinics run by charities.

Find HIV testing services near you

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 medicine called post-exposure prophylaxis (PEP) may stop you becoming infected if started within 72 hours of possible exposure to the virus – it's recommended that you start it as soon as possible, ideally within 24 hours
• an early diagnosis means you can start treatment sooner, which can improve your chances of controlling the virus, reduce the risk of becoming more unwell and reduce the chance of passing the virus on to others

Both positive and negative HIV tests may need to be repeated 1 to 3 months after potential exposure to HIV infection (this is known as the window period), but you should not wait this long to seek help:

• clinics may offer a finger prick blood test, which can give you a result in minutes, but it may take up to a few days to get the results of a more detailed HIV test
• home testing or home sampling kits are available to buy 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.

Antiretroviral medicines are used to treat HIV. They work by stopping the virus replicating in the body, allowing the immune system to repair itself and preventing further damage.

These come in the form of tablets, which need to be taken every day.

HIV is able to develop resistance to a single HIV medicine very easily, but taking a combination of different medicines makes this much less likely.

Most people with HIV take a combination of medicines. It's vital these are taken every day as recommended by your doctor.

The goal of HIV treatment is to have an undetectable viral load. This means the level of HIV virus in your body is low enough to not be detected by a test.

If you're living with HIV, taking effective HIV treatment and being undetectable significantly reduces your risk of passing HIV on to others.

You'll also be encouraged to:

• take regular exercise
• eat a healthy diet
• stop smoking
• 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.

If you're planning on getting pregnant, it's important to talk to a GP. Although rare, it's possible to transmit HIV to your baby.

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

There are many effective ways to prevent or reduce the risk of HIV infection, including:

• using a condom for sex
• post-exposure prophylaxis (PEP)
• pre-exposure prophylaxis (PrEP)
• treatment for HIV to reduce the viral load to undetectable
• if you use drugs, never sharing needles or other injecting equipment, including syringes, spoons and swabs

Speak to your local sexual health clinic or a GP for further advice about the best way to reduce your risk.

For people with HIV, if you have been taking effective HIV treatment and your viral load has been undetectable for 6 months or more, it means you cannot pass the virus on through sex.

This is called undetectable=untransmittable (U=U).

NAM aidsmap: undetectable equals untransmittable (U=U) consensus statement