Pollen path: The stealthy science behind your seasonal allergy misery

Allergies are miserable. Your eyes water, your sinuses hurt, and your nose somehow turns into both a leaky faucet and a clogged drain.

The culprit? Depending on the season, it’s the trees, grass or weeds releasing pollen into the wind.

Your first allergy attack can seem to come out of nowhere. However, in many cases, your immune system has been preparing for it for years.

Every spring, for example, pollen drifts off trees and floats through the air. These grains can become trapped in the mucus that lines your eyes, nose, and throat. And for a while, your body doesn’t overreact.

But your immune system is doing detective work, sending its scouts — known as dendritic cells — to snag bits of this potential invader for analysis.

Scientists aren’t sure why, but at some point, your immune system starts treating this innocent piece of pollen as if it were a parasitic worm.

This case of mistaken identity leads your immune system to pump out chemical messengers called cytokines. These drive inflammation and activate the white blood cells that produce antibodies.

The antibodies are churned out and stationed on mast cells, which act as tiny land mines in your eyes, nose and airway — preparing your body for the next pollen invasion.

This is sensitization, the process by which your immune system learns to recognize pollen as a threat and arms itself for future attacks.

Approximately 25% of adults in the US have seasonal allergies. Sensitisation can occur after a single exposure or over several seasons. Some become sensitized in childhood; others after moving to a new region or experiencing an unusually high pollen count.

The next time pollen arrives, it might bind to the antibodies your body planted.

Pollen detonates these mast cells in your eyes, nose and airway. The result? A surge of inflammatory chemicals, including histamine.

Then the misery begins. Histamine makes nearby blood vessels leaky, allowing plasma and immune cells to seep out. This would help the body fight off a parasite, but with pollen, it just causes redness and puffy eyes.

All the inflammatory chemicals make you produce extra mucus to trap the pollen, leaving you with a runny nose and a cough as well.

Histamine also irritates your sensory nerves and makes you itchy. As a result, your eyes water to flush out the pollen, and you start sneezing to blast it out.

Hours later, white blood cells called eosinophils arrive as reinforcements, releasing another wave of chemicals that keeps tissues swollen and mucus flowing. This explains why symptoms linger. The ordeal can leave you tired and foggy; congestion disrupts sleep, and researchers believe allergic inflammation may even affect mood and memory.

Fortunately, treatments can interrupt this spiral. Antihistamines block cells from responding to histamine, while steroid nasal sprays quiet inflammatory signals to reduce swelling. Saline rinses help by physically flushing out irritants. Although changing seasons bring different pollens, understanding this internal "script" provides the best tools to fight back.

The New York Times