You cannot get HIV from sharing a cigarette because HIV is not passed by saliva. This is why it is not passed through kissing or sharing eating utensils either.
If there is old or dried blood on the cigarette, you will not get HIV because HIV does not live for long outside the body.
If there is a fresh blood and you had an open area (like a sore or cut) on your mouth, it is possible that you could get HIV. However, we do not see HIV being passed this way.
HIV is passed by blood, semen (including pre-cum), rectal fluids, vaginal fluids and breast milk. HIV can only be passed when the virus in one of these fluids gets into the body of an HIV-negative person. This can happen sexually during condomless vaginal/internal genital and anal/rectal sex. HIV is unlikely to be passed through oral sex or rimming. HIV can also be passed through sharing needles or other drug equipment. To learn more about how HIV and STIs are transmitted, see our ‘Know your chances’ page.