Leaving aside whether a particle-mask is a wise idea because of pre-existing known allergies (which you would already have known about), why would you have a dust cloud? Place the slightly opened packet a few millimetres above the water and shake-and-pour gently -- throwing the powders into the mixing container, in handfuls, from the other side of the room (possible slight exaggeration) is not a sensible way to proceed, even if you were only making a cake. Ingestion of the Xtol sounds as though it is unlikely to have caused your symptoms. In best practice, your protective equipment should be completely clean and sterilised before each use - this could well be a source of some fungal trigger for your illness.
Chemists: wouldn't whatever might be the cause of Peter's problem be produced in greater quantity if the mixing is done at a higher than necessary temperature?
