HIV is not passed on easily from one person to another, especially compared to other viruses. That's because the HIV virus is present in body fluids. So for HIV to be passed on, the body fluids of someone who is already infected have to get into an uninfected person's body and then into their bloodstream.

Main sources of infection

The body fluids that contain enough HIV to infect someone are:

 - seminal fluid
 - vaginal fluids, including menstrual fluids
 - breast milk
 - blood

Other body fluids, like saliva, sweat or urine, do not contain enough of the HIV virus to infect another person.

So the main ways that HIV can be transmitted are:

 - through sexual intercourse and other sexual activities
 - from mother to baby
 - from blood to blood

Sexual activities

HIV is found in semen and vaginal fluid and can be passed on through vaginal, anal and oral sex. The virus can also be present in the fluid that is released from the penis to help lubricate it during sex.

Anal and vaginal sex are the most common ways for HIV to be passed from an infected person to someone who doesn't have HIV. If you are going to have penetrative sex (which is when a man's penis enters someone else's body) then the most effective way of minimising the risk of HIV being passed from one person to another is to use a condom properly. A water based lubricant (never an oil based one) will reduce the risk of the condom tearing and make sex more comfortable.

Because the HIV virus is found in the fluid released before ejaculation, it is also important that the penis is covered with a condom before penetration and that this doesn't come off during sex. Relying on someone to withdraw their penis before ejaculation is not an effective way of preventing HIV infection.

There have been cases where someone has become infected through oral sex with an HIV positive man, where infected fluids from their penis get into the uninfected person's mouth. To reduce this relatively small risk you can use condoms for oral sex: some people prefer to use flavoured condoms for this.

From mother to baby

Babies can get HIV from their mothers, but these days this doesn’t happen often if precautions are taken during the pregnancy, during the birth and in the first months of the baby’s life. So women living with HIV can still get pregnant and have a baby that doesn't have HIV.

You can find out more about mother to baby transmission on the THT site here.

Blood to blood

Bleeding on its own isn’t enough to transmit HIV from one person to another. The blood of a person with HIV needs to get into an uninfected person's body for them to be at risk of HIV. This sometimes used to happen during blood transfusions and affected some people who regularly required blood products, such as haemophiliacs. However, in the UK since 1985/1986, all blood donations have been screened for HIV and blood products for haemophiliacs have been treated.

Another way that blood can be passed from one person to another is through shared needles. Some intravenous drug users (who take their drugs by injecting them) have become infected by sharing needles with others who have HIV.

The two ways that intravenous drug users can reduce the risk of HIV infection are:

 - always use fresh needles
 - never share drug equipment with anyone else.

This advice also applies to you if you inject steroids into your muscles.

Misconceptions about infection

You can't get infected with HIV through normal social contact or through many other actions thought by some people to be risky including:

- through unbroken, healthy skin
- kissing
- sharing cups, plates, cutlery or linen, such as towels
- using the same toilets and swimming pools.

Caring for someone living with HIV or AIDS does not put you at risk, and neither does mouth-to-mouth resuscitation. And you can't breathe it in or get infected by mosquitoes or other animals.