I get asked about my mask a bunch on the street. Honestly I've default to pointing to the trees and saying "allergic" which is true (MCAS, so allergic to everything under the sun including the sun) but not the only reason I wear a mask
So if anyone wants an excuse, feel free to use that, even if you're not allergic. People should keep their noses out of your mask, so I think giving a short answer is the best, even if its not true. They are not owed any reason just because they ask