Do not misunderstand me - many of your habits are truly disgusting and the nanites are probably the only reason you haven’t dropped dead of a heart attack by now.
Your “cloud” is composed mainly of exhaust: heat and ash, mostly, along with any stray particles taken in. Currently you should only experience this side effect while overclocking the nanites en masse - i.e. pushing your body past its physical limits. If this is occurring regularly without strenuous activity, please come see me.
The “cloud” may also contain a number of the nanites themselves. This is an intended function that assists them in obtaining reconnaissance data; they will return to you eventually.
I frankly never thought to test the effects of inhalation, as you do not actually use your lungs. I, too, would be interested in the results of such a study, and will be sure to have the necessary equipment ready for your next examination, with your permission. To make an educated guess: I would not recommend regular exposure. It’s similar to inhaling smoke from a burning corpse, chemically, and while a small number of stray nanites exiting a foreign host’s body would likely be unnoticeable, a larger population may cause mild to severe pain, depending on their number and chosen exit route.