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Outdoor Allergens

Seasonal allergic rhinitis, also called hay fever, is characterized by nasal congestion, itchy watery eyes, sneezing, headache and discomfort.  It affects more than 35 million Americans each season. Seasonal rhinitis (hay fever) and seasonal exacerbations of asthma are most commonly provoked by airborne pollens and mold spores. During the spring and fall, those who suffer from seasonal hay fever, allergic rhinitis and asthma experience increased symptoms, including sneezing, congestion, a runny nose, and itchiness in the nose, roof of the mouth, throat, eyes and ears-depending on where they live and the allergen to which they are allergic.

Pollens microscopic granules that contain the male cell of plants. Trees, weeds and flowering plants send out pollen in order for fertilization.  Waxy pollens, like those found in flowering pants such as daisies, do not usually precipitate allergic responses in people. These pollens are designed to be carried on the backs of bees and other insects and the waxy coating that makes them stick to the insect also makes them heavy.  Unlike their flowering cousins, trees, grasses and weeds produce light dry pollens which are easily dispersed in the wind.  These are the pollens that tend to cause allergic symptoms. 

Each plant has its own pollination cycle.  These vary by species, but do not vary from year to year. Some species will predominate on one region and some in another, so allergic symptoms in people will vary depending on where they live.  People who suffer from hay fever (rhinitis) in the spring are most likely sensitive to one or more of the following trees:  Oak, western cedar, elm, birch, ash, hickory, poplar, sycamore, maple, cypress or walnut.  People who suffer in the late spring may be allergic to grasses, including: timothy, bermuda, orchard, sweet vernal, re top or blue grass.   Hay fever in the late summer or early fall is commonly due to ragweed, sagebrush, pigweed, tumbleweed, Russian thistle or cockleweed.

While the pollination schedule for most plants does not vary from year to year, weather conditions and rain fall may vary dramatically.  This can have a significant affect on the timing and the severity of the pollen season and may affect the amount of pollen circulating in the air at any given time. However, weather conditions can affect the amount of pollen in the air at any given time. The pollen season starts varies by region (climate) and may begin as early as January in the deep south, and as late as May in the north.  On average, the pollen season last through March to October. In general, trees pollinate earliest, in the spring, grasses follow, late spring to mid-summer and weeds usually pollinate in late summer and early fall.

Molds are tiny (microscopic) creatures related to fungi (mushrooms). Mold spores are the equivalent of mold seeds.  They disperse in the air much like tree pollens, but do not have a consistent season.  Weather conditions and temperature affect when mold will release spores.  In warm climates, mold may release spores year round.  In colder climates, spores are released after the winter thaw and peak mid-summer.  Some common molds include aspergillus, alternaria and cladosporium.  Molds can be found outside in soil, vegetation, on rotting wood or inside in damp places such as basements and bathrooms. 

Effects of weather and location

Weather can have a significant impact for people with allergic disease who suffer from sensitivity to outdoor allergens, because pollen and mold spores may be removed from the air by a heavy rain, whereas a dry wind will disperse an increased number of pollen and mold spores into the air. 

If you are allergic to plants in your area, you may believe that moving to another area.  However, most pollens and molds are found throughout the United States.  And people who are sensitive to one type of pollen are at increased risk of acquiring allergic sensitivity to other plant pollens.  Appropriate therapy, rather than a change in location, is the best method of dealing with allergic sensitivities.  If you suffer from seasonal allergies or hay fever, your allergist will take a detailed history to determine which plant pollens in your area may be the cause of your symptoms.  Allergy testing, such as prick testing may be  used to determine which pollen sensitivities are causing the allergic symptoms.  Your allergist may prescribe medications, such as nasal spray, antihistamines or decongestants to help you cope with your allergy symptoms.   If your symptoms are severe or persistent, your allergist may recommend immunotherapy treatment (allergy shots) to help your immune system develop a tolerance to the triggers of your symptoms and diminish your need for medications in the future.

Pollen and mold counts
Pollens and molds represent the clinically most important outdoor allergens. For the approximately 35 million Americans who suffer from seasonal allergies, rising counts in the spring can trigger symptoms that may ruin a time of year that other people enjoy immensely. 

The Aeroallergen Monitoring Network, organized by the American Academy of Allergy Asthma and Immunology, has compiled pollen counts for more than 30 years. The network has reported pollen and mold spore counts since 1992 through the National Allergy Bureau.

The information is reported as total tree pollen, grass pollen, weed pollen and mold spore counts.  Since allergic symptoms correlate with exposure, the information is invaluable in correlating allergic symptoms with the causative agent.

Further, trends in pollen counts, which may be predicted from prior years, may assist individuals who suffer from seasonal allergies, asthma and other allergic diseases associated with outdoor allergens to predict seasonal symptoms. 

Dos and don'ts
Following are some suggested methods of decreasing your exposure to outdoor allergens in order to reduce the severity of your allergic symptoms, like hay fever:


Keep windows closed at night to prevent pollen and spores from drifting into your home.  For ventilation, use air conditioning, preferably with an appropriate filter.

Minimize early morning exercise, since pollen counts tend to be highest up until 10 a.m.

Keep your car windows rolled up when traveling.

Stay indoors when pollen counts are high, on dry windy days.

Take vacations during the peak pollen season, in places where pollen counts are low (such as beaches or sea side resorts).

Consult your allergist regarding the best course of treatment for you.


Take more medication than recommended in an attempt to lessen your symptoms.

Mow the lawn (this stirs up pollen mold) or be around fresh cut grass.

Rake leaves (which also stirs up pollen and mold).

Hang clothing on clotheslines outside; pollens or mold spores may collect on them.

Keep plants indoors.

Over water plants in your garden, since wet soil can increase mold.

When to see an allergy and asthma specialist

Patients should see an Allergist if they or a family member:

• Need education and/or and management of the environmental triggers of their allergic disease.
• Are experiencing seasonal or persistent asthma, nasal or eye symptoms.
• To discuss treatment options, including immunotherapy (allergy shots).

Copyright © 2008-2010 Dr. Beth Cowan