Allergies are your immune system's overblown reaction to something it thinks is harmful (whether it actually is or not), so many symptoms associated w/colds, flus & systemic illnesses can also be attributed to allergic reactions... Rheumatoid arthritis is an allergic inflammatory reaction, as are certain types of lupus, celiac disease, IBS, etc. & so forth.

(I actually 'gave up' & started getting immunotherapy - and I wish I'd done it when I first got my health insurance 4 years ago. I started the shots in February, and I've taken maybe 4 Benadryl in the past 7 months. Right now, here in Vegas, something is blooming - my husband & most of my coworkers are miserable, but I can breathe through my nose & my eyes & ears & throat don't itch and none of my joints feel like they're full of hot ground glass. It's been pretty enjoyable. I can even roll around in fresh cut grass & not itch afterwards!)