HIV is not transmitted in the common ways that many other viruses are propagated by. This is due to the fact that the virus is very unstable and can easily break down outside of certain fluids. Laboratory studies show that when dried, HIV dies at high speed. The only liquids that HIV can survive well in are bodily fluids such as blood, semen, vaginal fluid, and breast milk. It follows from this that HIV can only be transmitted by blood-to-blood or other fluid-to-fluid contact.

The methods of transfer are sexual intercourse, an infected mother nursing a child or having a child in her womb, by sharing needles, or through blood transfusion. The first is the most common reason for HIV propagation among adults. Most children with the virus have it because their mother also was infected. The inadvertent transfer of HIV by using the same injection needle is most common among users of drugs such as heroin, and is yet another reason to stay drug-free. Blood transfusion almost never transmits the disease in the US, as there are screening procedures in place specifically to stop diseases like HIV. However, it remains a problem in less developed countries.

There has been some question as to whether HIV can be transmitted through kissing. With most kisses, this is not a problem. However, it is possible that HIV can be transferred through French or open-mouth kissing, although it is not probable. HIV can not be transferred through casual contact. Without the fragility of the HIV virus, it would be a much more dangerous disease, as it would be transferred in many more ways. With the knowledge of how hard it is to catch HIV, the simplest way to stay safe is to avoid dangerous situations like the above.