Why do many grasses and trees cause seasonal pollen allergies?

Grasses and trees that cause seasonal allergies, often referred to as hay fever, rely on wind pollination (anemophily) for reproduction. Unlike insect-pollinated plants that use fragrance or nectar to attract specific pollinators, these plants produce vast quantities of lightweight, dry, and smooth-surfaced pollen to ensure that at least some grains reach the stigmas of other plants by chance.1

Because wind pollination is a highly inefficient and wasteful process, these plants must release massive amounts of pollen into the air to be successful. This high concentration of airborne pollen is what triggers allergic reactions in sensitive individuals. When inhaled, the pollen causes the immune system to release histamine, leading to symptoms such as sneezing, nasal congestion, and eye irritation.12

Common culprits include grasses and various trees like oak, birch, and hazel, which often release their pollen in large quantities during specific seasons. While some people mistakenly blame conspicuous, insect-pollinated flowers like goldenrod for their allergies, the primary causes are typically these inconspicuous, wind-pollinated species.123