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.