What is the White Dust I see?
If you have a down comforter, chances are the fabric has been treated with a non-allergenic starch to fill the gaps in the weave. This ensures that the down filling does not spill out. As the fabric is washed and worn, the weave will naturally tighten, releasing the starch a bit at a time. If you see white dust shedding from your down comforter, this is actually a good sign it means your comforter is aging well and that the fabric is becoming stronger.