Why is saliva not a good carrier of HIV?
On what it is about saliva that does not make it a good carrier of HIV, saliva has been shown to possess many factors that have an anti-HIV effect. It is a combination of things. First, saliva has anti-viral, anti-bacterial and anti-fungal activities.
In addition, HIV induces the tissues lining the mouth to secrete small peptides and proteins that are capable of killing HIV. That said, you should keep in mind that there is still some risk of oral transmission of HIV if infected semen, blood or vaginal fluids enter the mouth, particularly in the presence of minute cracks in the mouth or with unhealthy gums. The saliva will not necessarily kill the HIV in these fluids.