If allergies are basically a pure immune response – no actual pathogen, just your body mistaking something harmless for a pathogen and freaking out – why does getting hayfever have distinct symptoms that most illnesses don’t have? Why does my immune system being set off because of harmless grass seed and pet dander give me itchy eyes and hives, but when it’s set off by a real virus it doesn’t do either of those things? On its face, shouldn’t being sick feel like “all the symptoms you get during an allergic reaction + whatever symptoms are caused by the actual harm the pathogen is doing”?
In: Biology
Allergens are actual physical things just like “real” pathogens. They get inside your body and so some times your body reacts to them, even if they don’t need to. Also. your body’s immune response is very localized. So your allergy symptoms are always going to be based on that location of the harmless pathogen. If the pet dandruff gets in your eye, your eyes get itchy. You breathe in plant matter, you get post nasal drip so on and so forth.
Actual illness causing pathogens do the same thing. Virus in your lungs? You cough and generate mucus. Intestinal parasite? Diarrhea, vomiting, gas, upset stomach etc. The difference is, actual illness causing pathogens have the ability to reproduce and move around. This makes them much more severe because your body detects much more of them and they stick around longer. (This is also an extreme simplification but ELI5).
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