Note: this site last updated in 2006
HIV and saliva
An article from "The Molecules of HIV" (c) Dan Stowell
Occasionally I'm asked about whether HIV is present in an HIV-positive person's saliva, and whether it carries a risk of transmission.
The short answer is that saliva virtually never carries any infectious HIV at all.
It does carry detectable "components" of HIV (such as viral RNA and proviral DNA), but these are not infectious on their own. The environment that saliva provides is far too harsh for infectious particles to remain intact and viable.
There are a number of possible mechanisms that have been suggested, which might explain why saliva seems to be so good at destroying HIV. Specific enzymes present in saliva may be important, or the effect of antibodies in saliva. Additionally, the saliva is "hypotonic" and has a tendency to disrupt any cells which may be floating around in it. It's pretty much certain that it's the combination of these factors that mean HIV is not transmitted in saliva.
It may seem strange that such a dangerous virus can't survive in something as "harmless" as saliva. In fact, saliva is a part of the body's natural defences against infection. Additionally, remember that the HIV virus is actually quite fragile.