There is no risk of passing on HIV through kissing and there is no HIV in saliva. Because of this, lots of people find it confusing that you can use oral samples to test for HIV.
To explain this, the first thing to know is that oral HIV tests do not detect the virus itself, instead they look for antibodies. These are cells that the immune system develops to respond to an HIV infection. So, oral fluids don’t contain the virus needed to pass HIV on, but they do contain the antibodies required to detect an HIV infection.
It’s also worth noting that the tests do not look for antibodies in saliva, instead they test something called ‘oral mucosal transudate’, which is a fluid that is released from the cells that make up your cheeks and gums. This is why when you take an oral sample you rub the stick along your gums and cheeks, where antibodies are more likely to be found.