Hay fever (Allergic Rhinitis) is the most common of the allergic diseases and refers to seasonal nasal symptoms that are due to pollens. One of the most obvious features of pollen allergy is its seasonal nature; people experience symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Plants produce microscopic pollen grains to reproduce. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross-pollinated; that is, in order for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another plant of the same species. In-sects do this job for certain flowering plants, while other plants rely on wind transport. The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants that do not have showy flowers. These plants manufacture small, light, dry pollen grains that are ideal wind transport. Because airborne pollen is carried for long distances, it does little good to rid an area of an offending plant as the pollen can drift in from many miles away. Among North American plants, weeds are the most prolific producers of allergenic pollen. Rag-weed is the major culprit; a single ragweed plant can generate a million grains of pollen a day. Colorful or scented flowers have large, heavy, waxy pollen grains. This type of pollen is not carried by wind but by insects such as butterflies and bees, and is not typically a cause of seasonal allergy. Similarly, the heavy, very visible pine pollen, is usually not a significant cause of symptoms.
A pollen count is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is expressed in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods.
Controllers – Leukotriene Antagonist
Download this article as a PDF