I use Gem White Shaving it is made from Hemlock and Douglas Fir I have had no issues with rat sneezing from it. The shaving come in a 4cu.ft. bundle and are not terribly expensive. Last time I purchased some it was about $13 you have to buy it at a feed store most people use it for horse stalls but works great fro rodentsI would also look at ventilation you my need to clean a little more often or ventilate your space a little better.