SERIOUSLY!! I left Philadelphia in 1992. I had hay fever every October for about 2 weeks. I've had "hay fever" since October 1992. My nose is just a decoration on my face!! Multiple allergy tests later and the doctors could only come up with "non-allergic rhinitis" or "vasomotor rhinitis." On the positive side, I am very allergic to red cedar, MAJOR hives, itching, and grab-the-ice-pack-do-we-need-the-epipen-call-an-ambulance type reaction. I don't think that nurse will EVER leave a patient alone in a room while testing for allergies again. (Injection of Benadryl cured what ailed me.) It was fun watching the crap hit the fan that day. It was not fun walking around with a hive the size of a basketball on my arm for a week. That allergist didn't do the back scratches. He injected minute quantities of the allergen under your skin on the insides of your arms and checked the reactions. They checked the initial reactions, after three minutes, after five minutes and after 10 minutes. My initial reaction was fine. By three minutes I was screaming, "UH, hello? Can somebody help me!!" She had gone to get me a can of soda. I think she took a lot longer than "three minutes."
ANYWAY. I would suggest you make sure with his doctor before you try the menthol to ensure it's not going to irritate his lungs. Also, if the doctor says OK, maybe try the pan of water with the menthol crystals? The nice thing about that is it releases the smell into the house and the benefits last longer than "just" a shower. So, he's not confined to one room. Also, I am able to re-use the crystals several times before they run out of power. Then again, if no one else in the house wants to smell the menthol, I can understand why you'd not want to do the hot water thing. But, putting some crushed crystals into a heat-save bowl and pouring boiling water on top of them would give the same effect in a smaller area.