A defence aimed at nothing
Why Does Pollen Make Some People Sneeze?
An allergy is your immune system running a full attack on something completely harmless.
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Step 1 of 5
Your immune system has to guess.
It cannot know in advance what is dangerous, so it learns by flagging things it meets. Occasionally it flags something entirely harmless.
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Step 2 of 5
The flag is stored on cells full of chemicals.
Antibodies against that pollen are parked on mast cells, which sit in your nose, eyes and airways stuffed with histamine and waiting.
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Step 3 of 5
Next time, they all fire at once.
Pollen binds the antibodies, the cells dump their contents in seconds, and histamine widens vessels, leaks fluid and irritates every nerve nearby.
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Step 4 of 5
Every symptom is a defence doing its job.
Nothing here is malfunctioning. It is simply aimed at the wrong thing. Runny nose flushes the invader out. Sneezing blasts it away. Swelling and itching bring more defenders. All of it is useful — against something real.
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Step 5 of 5
Antihistamines block the messenger, not the pollen.
They do not remove the pollen or unteach the mistake. They stop histamine from being heard, which is why they work best taken before exposure.
Pollen grains from wind-pollinated grasses are tiny and made in enormous numbers — a single rye plant can release several million grains in a day.
The short version
An allergy is a real immune defence aimed at something harmless, and every symptom you feel is that defence rather than the pollen itself.
Try it yourself
Notice that hay fever is worse on dry, windy days. There is more pollen in the air — the defence has not changed, the trigger has.