These additional questions are meaningless. I would encourage you to not worry or even think about the biological reasons that such transmission doesn't occur. The fact is that NOBODY ever caught HIV from such exposure. For example, people living in the same home with someon with HIV never get infected themselves (assuming they are not also sex partners of the infected persons) -- even after 10 years or more sharing the same bathrooms, kitchens, towels, eating utensils, and beds. The scientific reasons don't matter -- it just doesn't happen.
There is no additional information you can think of that would possibly change my opnion or advice -- so I won't have anything more to say. This thread is over.
Dear doctor,
Thank you for your answer. I have some question about it. It need enough virus to get infected. But if it is not enough, the virus can be killed by the immune system of human body? Or what is the result of the virus? Somebody said it need 200ul.
Can you tell me for other reason to the no risk conclusion. Can I think this way, the blood in the dandruff is so little that the virus lose infection as soon as exposed to air. I know eating is a no risk way, but I couldn't find other same question for the inhaling. Thank you again.
Welcome to the forum.
There is absolutely no risk of HIV from this sort of contact. If HIV could be transmitted by sharing a lift with an infected person (or by other day-to-day contact, like shaking hands, sharing a bus or train, and so on) AIDS would be a hundred times more common than it is and it would not be classified as a sexually and blood-borne infection. Even doctors and nurses taking care of HIV infected persons never catch the virus unless they have serious contact with the patients' blood (i.e. injuries by instruments contaminated with blood). You cannot catch HIV by inhalation.
And it is true that it takes a lot of virus to transmit HIV. That's one of the reasons that contact like you describe is no risk.
So don't worry about this. To avoid HIV for your entire life, all you need to do is always have safe sex, and do not share drug injection equipment with other people. There are no other possibilities you need to worry about.
Best wishes-- HHH, MD