Hello and thank you for posting your medical question on E health forum.
HIV is transmitted by direct contact with bodily fluids including contact with infected blood. In presence of cuts, sores, open wounds, the risk of transmission increases.
In this specific case, it would depend on the amount of blood involved, the period lapsed before the use of cigarettes by both individuals involved, the presence of infection in either of you and the presence of oral lesions.
HIV virus does not exist outside the living cells, and is immediately rendered noninfective. Also transmission of HIV via fomites has not been detected or proved to be causative of HIV infection, hence is not a risk.
If you still have doubts, you might consider to consult with your doctor who can provide reassurance and also can clear all your doubts that you may have.
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