I think it's gotta be something with the birds or small mammals...I don't do anything with the fish, and never have any issues while working with the reptiles. I'd experiment to see if I could narrow it down to either bedding or the animals, but I'm not sure how other than changing the bedding. And Carefresh is the best thing we can use for the mammals, so I don't want to do that. I have a feeling it might just be due to how dusty the Carefresh is though...I've not had it get any worse while actually handling the animals. But I've also never been allergic to anything, so I dunno how it works.