Sneezing Was sneezing, now it has stopped. Dust? Allergies?

A few weeks after I first got Shadowfax, he started sneezing several times a day. I watched him very closely for a couple of days, and he had no other symptoms at all. He was eating, drinking, running, popcorning, and being friendly. His eyes, ears, and nose looked normal. His cage was half fleece, half Carefresh natural bedding. I washed his fleece with Free & Clear laundry soap, and changed his bedding to the less dusty white Ultra Carefresh bedding. He has not sneezed since and it has been almost a week. He's acting totally normal. Do you think it was just an allergy or dust? Should I still be concerned? Thanks for reading!