Dr. Williams and other vets have written about this in the past but...
 
I would recommend avoiding pine and cedar chips.  I know of a breeder who
uses aspen chips which don't have the aromatic oils of the evergreens.  I
don't know why anyone would want messy woochips in their house.  Ferrets
are just as happy with old sweatshirts.  You can even wash the shirts and
use them over and over.  They won't get flung out of the cage and have to
be swept up.  You could use corn cob litter as bedding (no aromatic oils
there either) but it is just as messy as the wood chips.
 
bill and diane killian
zen and the art of ferrets
[Posted in FML issue 1200]