Nasal allergies and asthma are similar conditions in different parts of the
- As many as 78% of asthma patients have nasal symptoms.
- As many as 38% of nasal allergy patients have asthma.
- Treating the allergic inflammation in the nose may help prevent asthma
or reduce asthma severity and lower airway hyper-responsiveness.
Each spring, summer, and fall, tiny particles are released from trees, weeds,
and grasses. These particles, known as pollen, hitch rides on currents of air.
Although their mission is to fertilize parts of other plants, many never reach
their targets. Instead, they enter human noses and throats, triggering a type
of seasonal allergic rhinitis called pollen allergy, which many people know
as hay fever or rose fever (depending on the season in which the symptoms occur).
In some people with asthma, pollen can trigger their asthma symptoms. However,
pollen is not as likely to trigger asthma as indoor culprits, like dust
mites, mold, and animal
What is pollen?
Plants produce microscopic round or oval 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. Insects 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 (trees, grasses, and weeds) that do not have showy
flowers. These plants manufacture small, light, dry pollen granules that are
custom-made for wind transport. Samples of ragweed pollen have been collected
400 miles out at sea and 2 miles high in the air. Because airborne pollen is
carried for long distances, it does little good to rid an area of an offending
plant -- the pollen can drift in from many miles away. In addition, most allergenic
pollen comes from plants that produce it in huge quantities. A single ragweed
plant can generate a million grains of pollen a day.
The chemical makeup of pollen is the basic factor that determines whether
it is likely to cause hay fever. For example, pine tree pollen is produced
in large amounts by a common tree, which would make it a good candidate for
causing allergy. The chemical composition of pine pollen, however, appears
to make it less allergenic than other types. Because pine pollen is heavy,
it tends to fall straight down and does not scatter. Therefore, it rarely reaches
Among North American plants, weeds are the most prolific producers of allergenic
pollen. Ragweed is the major culprit, but others of importance are sagebrush,
redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English
Grasses and trees, too, are important sources of allergenic pollens. Although
more than 1,000 species of grass grow in North America, only a few produce
highly allergenic pollen. These include timothy grass, Kentucky bluegrass,
Johnson grass, Bermuda grass, redtop grass, orchard grass, and sweet vernal
grass. Trees that produce allergenic pollen include oak, ash, elm, hickory,
pecan, box elder, and mountain cedar.
It is common to hear people say that they are allergic to colorful or scented
flowers like roses. In fact, only florists, gardeners, and others who have
prolonged, close contact with flowers are likely to become sensitized to pollen
from these plants. Most people have little contact with the large, heavy, waxy
pollen grains of many flowering plants because this type of pollen is not carried
by wind but by insects such as butterflies and bees.
"I love springtime, but the pollen drives me up the wall! I start
taking my medication as soon as I see buds on the trees."
-- Esther, age 39
When do plants make pollen?
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. Exactly when a plant starts to pollinate seems
to depend on the relative length of night and day -- and therefore on geographical
location -- rather than on the weather. (On the other hand, weather conditions
during pollination can affect the amount of pollen produced and distributed
in a specific year.) Thus, the farther north you go, the later the pollinating
period and the later the allergy season.
A pollen count, which is familiar to many people from local weather reports,
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.
Although a pollen count is an approximate and fluctuating measure, it is useful
as a general guide for when it is advisable to stay indoors and avoid contact
with the pollen.
- Avoid the outdoors between 5 - 10 a.m. Save outside activities for late
afternoon or after a heavy rain, when pollen levels are lower.
- Keep windows in your home and car closed to lower exposure to pollen. To
keep cool, use air conditioners and avoid using window and attic fans.
- Be aware that pollen can also be transported indoors on people and pets.
- Dry your clothes in an automatic dryer rather than hanging them outside.
Otherwise pollen can collect on clothing and be carried indoors.
Created by the National Institutes of Health. Updated and modified by A.D.A.M.,
Inc. Illustration copyright A.D.A.M., Inc.
American Academy of Allergy, Asthma & Immunology (AAAAI). The Allergy
Report: Science Based Findings on the Diagnosis & Treatment of Allergic
Disorders, 1996-2001. Milwaukee, Wis: American Academy of Allergy, Asthma & Immunology
(AAAAI); 2001. (2007 updated version available online at www.theallergyreport.com.)
Review Date: 5/16/2007
Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc.
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