What is the best way to block cigarette smoke from the body? Would it be better to hold your breath after smelling the presence of it or quickly inhale and exhale to get rid of it in your system(body)? EDIT: Changed from carbon monoxide to cigarette smoke.

You don't smell carbon monoxide in cigarette smoke. It's odorless. (And not exactly the part of cigarette smoke I would be worried about.)

You smell the _other_ components of cigarette smoke. Which are _not_ odorless.

Holding your breath and getting out of the smoke seems the way to go. Even better would be **ex** haling, then holding your breath until you are clear.[1]

Carbon monoxide, as well as other components of cigarette smoke like nicotine, are very good at getting into your blood stream quickly. Plus, when at rest, we inhale / exhale at only a fraction of our lung capacity. By (deeply) **in** haling (your alternative course of action), you would just get _more_ of the smoke into your lungs than you already have.

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[1]: The trick with holding your breath is of course that, if you run out of breath while still in the middle of the smoke, you can't _help_ but inhaling deeply...