Pollen is the male fertilizing agent of flowering plants, trees, grasses and weeds. It is also a major allergen that causes symptoms of seasonal allergic rhinitis (hay fever)*. Weather conditions affect pollen levels. For instance, wind and humidity may affect pollen counts. Because pollen are small, light and dry, they can be easily spread by wind, which keeps pollen airborne and carries it over long distances. When the air is humid, such as during or after it rains, pollen becomes damp and heavy with moisture, keeping it still and on the ground. Allergy symptoms are often minimal on days that are rainy, cloudy or windless, because pollen does not move about during these conditions. Hot, dry and windy weather signals greater pollen and mold distribution and therefore, increased allergy symptoms.
Pollen from plants with bright flowers, such as roses, usually does not trigger allergies. These large, waxy pollen are carried from plant to plant by bees and other insects. On the other hand, many trees, grasses and low-growing weeds have small, light, dry pollen that are well-suited for dissemination by wind currents. These are the pollens that trigger allergy symptoms.