Pollen causes allergies because your immune system mistakes it for a dangerous germ and launches a full-blown defense response against it.

What pollen actually is

Pollen is a fine powder released by plants (especially trees, grasses, and weeds) to reproduce; it’s meant to reach other plants, not your nose.

For most people it’s harmless, but in people with “sensitized” immune systems, it becomes an allergen that triggers symptoms like sneezing and itchy eyes.

How your immune system overreacts

When someone with a pollen allergy inhales pollen, their immune system misidentifies the pollen proteins as a serious threat, similar to a virus or bacteria.

In response, the body produces a special antibody called immunoglobulin E (IgE) that specifically recognizes that type of pollen.

These IgE antibodies attach to immune cells such as mast cells in your nose, eyes, and airways.

The next time you breathe in the same pollen, it binds to those IgE-coated cells and triggers them to release chemicals like histamine.

Histamine and related chemicals cause blood vessels to leak fluid, nerves to become irritated, and tissues to swell, leading to symptoms such as sneezing, congestion, runny nose, itchy eyes, and sometimes asthma flare-ups.

Why some people get pollen allergies and others don’t

Not everyone’s immune system reacts this way; allergies develop when the immune system becomes “trained” incorrectly to see harmless substances as dangerous.

Genetics play a role (allergies often run in families), and environment matters too: lower exposure to microbes in early life may leave the immune system more prone to misfiring at things like pollen (the “hygiene hypothesis”).

Over time, repeated exposure to certain pollens (like grass or tree pollen) can sensitize someone so that even small amounts trigger symptoms during high- pollen seasons.

This is why people often notice allergies flare in spring or early summer, when pollen counts are high and seasons are becoming longer and more intense in many regions.

Why symptoms come and go

Pollen allergy symptoms are worst when the pollen you’re sensitized to is in the air in high concentrations, such as on dry, windy days during that plant’s peak season.

Rain, temperature shifts, and local plant types can all change how much pollen you’re exposed to on a given day, so you might feel fine one week and miserable the next.

Because the reaction depends on exposure plus your existing sensitization, people can also feel like allergies appear “out of the blue” after years without problems once their immune system has built up that IgE response.

TL;DR: Pollen itself isn’t harmful, but in people with pollen allergies the immune system wrongly flags it as dangerous, makes IgE antibodies, and releases histamine whenever pollen is inhaled, causing the classic hay fever symptoms.

Information gathered from public forums or data available on the internet and portrayed here.