HIV cannot be transmitted by sharing a cigarette, according to HIV Aware, which aggregates information from the United Kingdom's National AIDS Trust. HIV cannot be transmitted by this means even if the person sharing the cigarette has a cut lip or a cold sore.
HIV Aware states that HIV can only be transmitted if the virus enters the body and the bloodstream without being exposed to the environment. The fragility of the virus means that it does not survive exposure to the environment. Sex without a condom can lead to HIV transmission, as can sharing needles and intravenous drug equipment. Not all sexual activities have a high risk of HIV transmission. There is no risk of HIV transmission when mutual masturbation occurs, and the risk of HIV transmission via oral sex is much lower than with vaginal or anal sex.