Exactly; my fault for not thinking properly <adjusted>. Henrik Öhrström pointed out that mesoscale nanomachines might actually pose a hazard similar to silicosis or asbestosis by being fairly large structures the macrophages in the lung cannot handle. I seem to recall that the ufog designs involved inert foglets with silicon(?) shells; maybe they should be made vulnerable to the chemicals released by lymphocytes or other cells. Maybe some connectors made of protein, for example.
By the time ufog is a reality, wouldn't most people be chock full of tiny little (nano) robots which collected debris in the lungs / poisons in food / any other unruly stuff, and got rid of it? Why not, instead of trying to make ufog safe to digest, design a nano-robot scavenger that catches debris and takes it out of harm's way?
I swallowed a spider to catch the fly