Do I understand HIV?

Learning the facts raises your awareness of HIV and allows you to take better care of your own health


HIV (Human Immunodeficiency Virus) is a virus which attacks
the immune system - the body's defence against diseases.

HIV stays in the body for life, but treatment can keep the virus under control and the immune system healthy. Without medication people with HIV can develop AIDS.


AIDS (Acquired Immune Deficiency Syndrome) is the most advanced stage of an HIV infection when the immune system can no longer fight infections.

Someone with AIDS has both HIV and at least one of a specific list of 'AIDS-defining' diseases, which include tuberculosis, pneumonia and some types of cancer

AIDS is life-threatening, but if HIV is caught early and is treated, it will not lead to AIDS. If HIV is caught late, it can lead to more complications and could ultimately lead to AIDS. That is why it is so important to get tested early if you have been at risk of HIV, as it will mean that you can access treatment that will prevent you from ever getting AIDS.

CD4 count

CD4 count is a measure of immune function. By measuring someone's CD4 levels you can see how HIV has affected their immune system, showing how far the virus has progressed.

Viral load

Viral load is a measure of how much HIV is in someone's body. The higher the viral load the more infectious someone is.


HIV medication increases a person’s CD4 count and reduces their viral load. Treatment is now so effective that it reduces someone’s viral load to undetectable levels within about 6 months, maintaining a healthy immune system and ensuring that they cannot pass on the virus.

There is, however, no cure for HIV and, once infected, a person has HIV for life.

Find out more about HIV treatment

How is HIV passed on?

    HIV can be passed on through infected semen, vaginal fluids, rectal secretions, blood or breast milk.

    You can get HIV from:

    • Vaginal or anal sex without a condom if your partner has an unknown HIV status, a detectable viral load and you aren't taking PrEP - high risk
    • Sharing injecting drug equipment -high risk
    • Oral sex -low risk

    A woman can pass HIV on to her baby in the womb, during childbirth
    and from breastfeeding, though effective HIV medication makes this extremely unlikely. 

      You can't get HIV from:

      • Sex with a partner who has HIV but is on treatment and has an undetectable viral load (learn more about undetectable equals untransmittable, U=U, here)
      • Touching, hugging, shaking hands or sharing utensils
      • Kissing, spitting or sharing saliva
      • Urine or faeces
      • Biting or scratching
      • Insect bites
      • Contact with a discarded needle

      Oral sex

      There is a very low risk of transmitting HIV through oral sex - both through fellatio (blow jobs) and cunnilingus (going down on a female partner).

      The risk of getting HIV through oral sex is significantly lower than from anal or vaginal sex.  

      However there are several factors that make HIV transmission from oral sex more likely:

      • If the person performing oral sex has mouth ulcers, sores or bleeding gums

      • If someone has been recently infected with HIV

      • If someone has another sexually transmitted infection (STI) in addition to their HIV

      The type of oral sex also affects the amount of risk:

      • Performing oral sex on a man with HIV carries some risk - particularly if he ejaculates (comes) in your mouth

      • Performing oral sex on a woman with HIV theoretically carries a risk, which is increased if she is having her period, but transmission is extremely unlikely

      • Receiving oral sex from someone with HIV carries a low risk

      For information about the risks of other sexual activities - including analingus (rimming) and fisting - visit NAM.

      HIV & travel

      In the past 10 years almost 2,500 UK-born people diagnosed with HIV in the UK acquired the virus while they were abroad.

      Many countries have much higher HIV rates than the UK, including countries in Sub-Saharan Africa, some parts of the Caribbean, Eastern Europe and South East Asia. There are also additional risks in other countries. In developing countries, for instance, 5-10% of HIV infections occur because of HIV-infected donated blood.

      It’s important to be especially careful of HIV when travelling abroad. You should take the same precautions everywhere as you would at home, including using condoms for sex and not sharing needles or drug equipment. When abroad you should also:

      • Weigh up the risk of having a blood transfusion in a developing country against the risk of further illness or death if the transfusion doesn’t go ahead

      • Insist on seeing a needle opened fresh from the packet if you need an injection
      • Take out comprehensive travel insurance before you leave

      I’ve been at risk of HIV

      If you think you have put yourself at risk of HIV, you should seek out local medical advice as soon as possible and get tested when you get home.

      Post-Exposure Prophylaxis (PEP), a short course of HIV treatment, can be taken if you are worried that you have acquired HIV. This treatment may stop you from getting HIV if taken within 72 hours after exposure. Access to PEP differs from country to country and may only be available in large cities rather than nationwide. Therefore you should not rely on this form of medication as protection from contracting HIV.

      Local HIV organisations might be able to advise you if PEP is available. You can find a list of HIV organisations here.

      Advice abroad

      To get in touch with a local HIV organisation visit HIV Lens - they have a comprehensive list of organisations on their website.

      You can also call the following UK numbers from abroad:

      If you would like to download a leaflet containing all this information and more please click here.