Sexually Transmitted Infections

If there is a drop of blood on a cigarette filter is it possible to get an STI or HIV from it?

Since HIV isn't found in saliva, you can't catch it through sharing a cigarette. This is why it cannot be transmitted through kissing or sharing eating utensils. You won't develop HIV if the cigarette has old or dried blood on it since HIV doesn't live long outside the body. It is possible to get HIV if there is fresh blood and you have an open wound on your tongue or mouth. However, because HIV dies relatively instantly when it comes into contact with air, this is exceedingly improbable. As a result, the virus cannot be transferred by the air or water.  HIV is only transferred or transmitted by contact with particular bodily fluids from an HIV-positive individual. Such fluids include those transmitted via sexual contact such as vaginal fluids, semen, pre-seminal fluids, rectal fluids, as well as blood and breast milk.