Pollens are the tiny, egg-shaped male cells of flowering plants. These microscopic, powdery granules are necessary for plant fertilization. The average pollen particle is less than the width of an average human hair.
Pollens from plants with bright flowers, such as roses, usually do not trigger allergies. These large, waxy pollens 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 pollens that are well-suited for dissemination by wind currents. These are the pollens that trigger allergy symptoms. Seasonal allergic rhinitis in the early spring is often triggered by the pollens of such trees as oak, western red cedar, elm, birch, ash, hickory, poplar, sycamore, maple, cypress and walnut. In the late spring and early summer, pollinating grasses - including timothy, bermuda, orchard, sweet vernal, red top and some blue grasses - often trigger symptoms.
In addition to ragweed - the pollen most responsible for late summer and fall hay fever in much of North America - other weeds can trigger allergic rhinitis symptoms. These weeds include sagebrush, pigweed, tumbleweed, Russian thistle and cockleweed. Each plant has a period of pollination that does not vary greatly from year to year. However, weather conditions can affect the amount of pollen in the air at any given time. The pollinating season starts later in the spring the further north one goes. Depending on where you live in the United States, the pollen season can begin as early as January (in the southern states). Generally, the pollen season lasts from February or March through October. Trees pollinate earliest, from late February through May, although this may fluctuate in different locations - starting in April in the northern United States to as early as January in the south. Grasses follow next in the cycle, beginning pollination in May and continuing until mid-July. Weeds usually pollinate in late summer and early fall.
Pollen and mold counts measure the amount of airborne allergens present in the air. Counts are compiled by a variety of methods. Pollen and mold spore counts can be determined daily, and are reported as grains per cubic meter of air. Certified aeroallergen counters at many universities, medical centers and clinics provide these counts on a volunteer basis.
The National Allergy Bureauï¿½ (NABï¿½) is the nation's only pollen and mold counting network certified by the AAAAI. As a free service to the public, the NAB compiles pollen and mold counts from certified stations across the nation and reports them to the media three times each week. These counts are also available on the NAB page of the AAAAI's Web site, www.aaaai.org.
Interpretation of pollen and mold counts and their relationship to symptoms is complex. Sampling techniques such as the type of device used and its location within the community can affect counts. While many patients develop symptoms when pollen counts are 20-100 grains per cubic meter, one's symptoms may also be affected by recent exposure to other allergens, the intensity of pollen exposure, and individual sensitivity. Pollen counts reported to the public are generally taken the preceding one to three days, and may vary widely from day to day during a season. Overall, the use of pollen counts in predicting symptom severity in a given individual is somewhat limited