I conjectured to a friend that some small amount of anything we smell is likely metabolized by the body. He disagreed. My thinking is that, if you are smelling something, some portion of molecules are being sensed by the olfactory tissue and some portion is taken into the lungs. Of the portion taken into the lungs, some portion is exhaled and some portion remains. I didn't propose a mechanism for the part that "remains" at the time, but it seems reasonable that some of it gets caught in mucus, some of which is then swallowed.
Obviously, a very, very small portion of whatever we're smelling would go through this process if my conjecture is even correct. For context, we were discussing people who have elected to restrict their diets for ethical or similar reasons. I was comparing what I proposed to when food products are labeled with "may contain trace amounts" due to "shared equipment".
So I guess my questions are these: was I right in my guess, and if so, was the mechanism correct or not?