Why do we lose immunity to viruses over time, but our immune response to allergens stays the same?
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Basically it’s like an attack dog. It’s response will be the same to any intruder that comes on the property (allergens/squirrels and actual viruses/theives) but will, given enough time forget about specific people it’s identified as an actual threat that it previously could identify by smell if it doesn’t see them for a long time.
To keep that metaphor going, allergens are like squirrels coming on the property – you know they are harmless, but your immune system attack dog will still treat them as a threat. And there are a lot more squirrels than thieves around.
Constant exposure to the same allergens as opposed to sporadic exposure to the same virus. Allergens are in the environment and are nearly impossible to avoid whereas a virus is far less common particularly to the point where you are exposed to a high enough viral load to trigger an immune response. If you are not repeatedly exposed to the same antigen you may lose immunity overtime as your body “forgets” how to fight it. IE you lose the memory immune cells.
Immune responses to allergens do change. They can get stronger or weaker over time, you can develop completely new allergies or even lose old ones.
Viruses change over time. You get a new stain of influenza virus every year. They evolve constantly and your immune system have to follow them up.
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