Ahhh, good on the Rainforest Mist! Brilliant minds and all that
Yes, at this point in time, an allergy would have shown the white blood cells that indicate inflammation elevated.
I also cannot have a humidifier running all day long, day after day, month after month in my living room and dining room. My husband loves me to pieces and never says no to me but he likes what he calls 'a normal family home' and he would most definitely balk at having the flooring, paintings and furniture destroyed by constant high humidity so I do the same thing: I spray them thoroughly (actually, some of them thoroughly and the others as best as I can running after them when they fly away from me) and wet the paper at the bottom of the cage - I actually soak it because it's under the grid so the birds don't ever step on it.
I don't believe is a habit, either, but, in all honesty, I am not sure... I guess that it can be taken as a form of feather destructive behavior. Lord knows they are as quirky as people when it comes to things like that so anything it's possible. I had a boss many years ago -an engineer from Texas who was the International Director of an OAS regionalization project for which I was the executive manager- who used to pull his eyebrows off by the roots! The man walked around with big holes in his eyebrows all the time.
Have you tried keeping a bottle of cool water by you and spraying him every time he scratches? I think I would try that.