Pollen
Pollen refers to the tiny grains or seeds released by flowering plants, trees, weeds, and grasses while they are blooming. Levels of pollen in the air are highest in spring and fall.
Exposure to pollen can cause allergic reactions like hay fever (allergic rhinitis), which results in sneezing, runny nose, and congestion; or allergic conjunctivitis, which causes red, watery, itchy eyes. Pollen can also worsen the symptoms of asthma and other respiratory illnesses.