For someone to get HIV, an infectious fluid like blood or semen has to get inside their body – usually during sex. This can happen if the person with HIV has a detectable viral load and no form of protection is being used.
How do you get HIV?
If someone with HIV is taking HIV medication and has an undetectable viral load they cannot pass on HIV.
If someone with HIV is infectious they can pass on HIV through the following body fluids:
This can be prevented by using a condom during sex, or by the HIV negative person taking Pre-exposure prophylaxis (PrEP) or Post-exposure prophylaxis (PEP).
People who inject drugs can avoid HIV being passed on by not sharing drug injecting equipment.
During pregnancy your doctor will advise you how to protect your baby.
How is HIV passed on during sex?
During sex body fluids from someone with HIV can get inside a person who is HIV negative.
If the person with HIV has a detectable viral load this allows the virus to enter the HIV negative person’s bloodstream. This can happen during vaginal and anal sex (and sometimes oral sex too though this is much less common).
It can also happen when an object (eg, a sex toy) that has infectious body fluids on it is put inside an HIV negative person.
When is a person with HIV infectious?
Someone with HIV is infectious if they have a detectable viral load.
This is often during the first few months after infection when they have very high levels of the virus in their body fluids and may not yet have been diagnosed.
Early diagnosis means you can start treatment to reduce your viral load to undetectable levels, prevent transmission to others and protect your health.
What is protected sex?
Protected sex means using a male or female condom during sex if one partner has HIV and a detectable viral load.
Condoms should be used with water-based lubricant, as oil-based lube weakens their structure.
HIV treatment is also a form of protection.
How HIV treatment stops HIV being passed on:
- A person with HIV who is taking treatment and has an undetectable viral load cannot pass on HIV.
- Pre-exposure prophylaxis (PrEP) is a course of HIV drugs taken by an HIV negative person to lower the chance of infection. When taken correctly, PrEP significantly reduces the chances of becoming HIV positive.
- Post-exposure prophylaxis (PEP) is a month-long course of HIV medication taken by an HIV negative person after possible exposure to reduce the chance of getting HIV. When started in time, PEP can stop HIV infection after sex without a condom (or other exposure) with someone who is infectious - but it does not work every time.
- If a woman is pregnant, HIV medication is part of the way mother to baby transmission can be prevented.
The PARTNER study
A large study called PARTNER looked at 888 gay and straight couples (and 58,000 sex acts) where one partner was HIV positive and one was HIV negative. Results found that where the HIV positive partner was on effective treatment and had an undetectable viral load, there were no cases of HIV transmission whether they had anal or vaginal sex without a condom.
The PARTNER study looked at couples where the HIV positive partner had a viral load below 200. An undetectable viral load is classed as being below 50 (although some tests can now measure below 20). However, before deciding to stop using condoms, it's a good idea to speak to your HIV doctor or nurse to make sure your viral load is undetectable.
It's also important to remember that if you have sex without a condom other sexually transmitted infections (STIs) can be passed on.
Sex without a condom can also result in an unplanned pregnancy if other contraception is not being used.
Can I get HIV without having sex?
Yes, HIV can also be passed on if you inject drugs and share injecting equipment (needles, syringes, swabs, spoons and other items) that has been used by someone with HIV.
A woman can give birth to a baby who also becomes infected. This could happen during labour but can also take place while breastfeeding or in the womb before the baby is born.
This is now extremely rare in the UK because the following medical interventions can reduce the risk of mother-to-baby transmission to below 1 per cent:
- the mother taking treatment if she is not already doing so
- she may be offered a Caesarian birth if her viral load is high
- the baby is given a course of antiretroviral treatment for the first few weeks
- the mother not breastfeeding.
In countries that don’t have strict checks on the safety of their blood supply (this began in the UK in 1985), receiving contaminated blood can pass the virus on. This could also happen in countries that don’t screen other blood products, organs or sperm.
Read more about different modes of transmission:
- HIV transmission through semen and vaginal fluid ››
- infected blood ››
- mother to baby transmission ››
- ways HIV is NOT transmitted ››
Symptoms of HIV infection ›› ››