I kinda squint at this skin brushing notion...even for me, its off the wall. The last little bit on digestive enzymes, now thats helpful, since its helps with immune system regulation.
See...this is another very old cellular regulation pathway..and is an important secondary role for digestive enzymes that you produce naturally and are present in some food sources. They regulate inflammation and repair response, toning down overactive inflammation and helping the body repair tissues (mostly skin, some connective / joint tissues as well.
Could be that the excess mucous and inflammation response affects gut, and that in turn, affects your gut's (via gut microbioat biosynthetic pathways) production of natural immune control agents. Might try probiotics and see if they help as well (look to oatbran, add to your shakes). Avoid use of stimulants, as they will make your allergy response and symptoms. Get your rest, avoid bulking and excessive saturated fats and carbs while you have these allergy symptoms.