I would definitely recommend using some sort of mask when doing anything that involves much bedding/DE dust. I didn't use to use a mask, but a couple weeks ago I was coughing/clearing my throat for several hours after stirring the bedding (to which I had added food grade DE). I don't think a couple times breathing the dust will kill you, but the cummulative effect could be significant, and by the time you realize you have a lung problem, it'd probably be too late. I use a mask something like this and it seems to work ok: http://www.amazon.com/Disposable-EA..._bbs_sr_1?ie=UTF8&s=hpc&qid=1225127035&sr=8-1 .