Pollen contains the necessary fertilizers for plant life to reproduce and grow. Unfortunately, when pollen is picked up in the wind, it can cause problems for a number of people who suffer allergic reactions when they inhale these particles through the mouth or the nose. Usually, the mucus in the nasal passages helps remove any irritants and sends them to the throat, where they are swallowed or expelled through coughing. For someone who is allergic, however, the particles trigger a reaction that causes cells in the nasal passages to release histamine, a chemical that essentially enlarges blood vessels in the nose. This, of course, causes nasal congestion.
Histamine is also responsible for sneezing, itching and irritation in the nasal and throat passages.
The largest producers of allergenic pollen in North America are weeds, such as ragweed, sagebrush or tumbleweed. Usually, bright flowers, like roses, are not causes of pollen allergies. The pollen from these plants is not windborne, but are carried from plant to plant by insects. Pollens from weeds, on the other hand, are designed to be carried by the wind to complete the fertilization process. Because such pollen can drift miles away from its original plant, escaping pollen is a nearly impossible task.