Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?
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The reason you react to allergens so acutely is because you have cells sat primed with antibodies ALREADY. Your body has seen the allergen (or something sufficiently structurally similar that it can’t tell the difference) before, and it is recognised by antibody that is already sat there waiting.
Whereas most infections that actually cause symptoms are ones your body has not met before. So it has to go through the entire process of mounting an acute response: releasing ‘attack cells’ that ‘eat’ the bacteria, ‘digest’ them and then ‘present’ identifiable bits of the digested bacteria to certain other specialised cells whose job it is to take those digested pieces, and start trying to create an antibody against the bug. It can take some time to find a decent antibody – and then after a good antibody has been identified, the body then has to mass produce it. Bacteria also have ‘cunning’ methods of circumventing this system, for instance by changing the identifiable elements of themselves, hiding them away, or actively neutralising the very cells that are involved in responding.
I think a reasonable analogy is to say it’s like trying to open a lock with a key when you already know which key you need, versus having no idea and having to try every single key on the keyring. And that some bacteria are then capable of switching/hiding the locks. Plus, some peoples bodies for whatever reason struggle to even make the keys in the first place!
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