it will be one of those unsolved mysteries. some say it is solvent, which it is not, some say it is the fina, which it is not, and some say pellet fillers & binders, which seems to be the only plausable cause. I have had cough with many high solvent gears, but only taste with fina pellets, never the powder.
interestingly, my worst coughs came from tren powder, but no taste.
Then, from fina pellets I get very strong taste, but no coughs. Go figure.