A sure sign of spring (or summer or fall) in many regions of the United States is news media reports of pollen counts. These counts are of interest to some 35 million Americans who get hay fever because they are allergic to pollen.
People also look for counts of mold or fungus spores. These are another major cause of seasonal allergic reactions. Pollen and mold counts are important in helping many people with allergies plan their day.
What Is the Pollen Count?
The pollen count tells us how many grains of plant pollen were in a certain amount of air (often one cubic meter) during a set period of time (usually 24 hours). Pollen is a very fine powder released by trees, weeds and grasses. It is carried to another plant of the same kind, to fertilize the forerunner of new seeds. This is called pollination.
The pollen of some plants is carried from plant to plant by bees and other insects. These plants usually have brightly colored flowers and sweet scents to attract insects. They seldom cause allergic reactions. Other plants rely on the wind to carry pollen from plant to plant. These plants have small, drab flowers and little scent. These are the plants that cause most allergic reactions, or hay fever.
When conditions are right, a plant starts to pollinate. Weather affects how much pollen is carried in the air each year, but it has less effect on when pollination occurs. As a rule, weeds pollinate in late summer and fall. The weed that causes 75 percent of all hay fever is ragweed which has numerous species. One ragweed plant is estimated to produce up to 1 billion pollen grains. Other weeds that cause allergic reactions are cocklebur, lamb's quarters, plantain, pigweed, tumbleweed or Russian thistle and sagebrush.
Trees pollinate in late winter and spring. Ash, beech, birch, cedar, cottonwood, box, elder, elm, hickory, maple and oak pollen can trigger allergies.
Grasses pollinate in late spring and summer. Those that cause allergic reactions include Kentucky bluegrass, timothy, Johnson, Bermuda, redtop, orchard, rye and sweet vernal grasses.
Much pollen is released early in the morning, shortly after dawn. This results in high counts near the source plants. Pollen travels best on warm, dry, breezy days and peaks in urban areas midday. Pollen counts are lowest during chilly, wet periods.
What Is the Mold Count?
Mold and mildew are fungi. They differ from plants or animals in how they reproduce and grow. The "seeds," called spores, are spread by the wind. Allergic reactions to mold are most common from July to late summer.
Although there are many types of molds, only a few dozen cause allergic reactions. Alternaria, Cladosporium (Hormodendrum), Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus and Aureobasidium (pullularia) are the major culprits. Some common spores can be identified when viewed under a microscope. Some form recognizable growth patterns, or colonies.
Many molds grow on rotting logs and fallen leaves, in compost piles and on grasses and grains. Unlike pollens, molds do not die with the first killing frost. Most outdoor molds become dormant during the winter. In the spring they grow on vegetation killed by the cold.
Mold counts are likely to change quickly, depending on the weather. Certain spore types reach peak levels in dry, breezy weather. Some need high humidity, fog or dew to release spores. This group is abundant at night and during rainy periods.
What Are the Symptoms for Hay Fever?
Pollen allergies cause sneezing, runny or stuffy nose, coughing, postnasal drip, itchy nose and throat, dark circles under the eyes, and swollen, watery and itchy eyes. For people with severe allergies, asthma attacks can occur.
Mold spores can contact the lining of the nose and cause hay fever symptoms. They also can reach the lungs, to cause asthma or another serious illness called allergic bronchopulmonary aspergillosis.
How Are Pollen and Mold Measured?
To collect a sample of particulates in the air, a plastic rod or similar device is covered with a greasy substance. The device spins in the air at a controlled speed for a set amount of time— usually over a 24-hour period. At the end of that time, a trained analyst studies the surface under a microscope. Pollen and mold that have collected on the surface are identified by size and shape as well as other characteristics. A formula is then used to calculate that day's particle count.
The counts reported are always for a past time period and may not describe what is currently in the air. Some counts reflect poorly collected samples and poor analytical skills. Some monitoring services give "total pollen" counts. They may not break out the particular pollen or mold that causes your allergies. This means that allergy symptoms may not relate closely to the published count. But knowing the count can help you decide when to stay indoors.
How Can I Prevent a Reaction to Pollen or Mold?
Allergies cannot be cured. But the symptoms of the allergy can be reduced by avoiding contact with the allergen.
The National Allergy Bureau tracks pollen counts for different regions of the country. To find out the counts for your region, go to the Asthma and Allergy page of our website, call (800)-9-POLLEN, or contact the bureau through the American Academy of Allergy, Asthma, and Immunology website.
Use central air conditioning set on "recirculate" which exclude much of the pollen and mold from the air in your home.
Vacationing away from an area with a high concentration of the plants that cause your allergies may clear up symptoms. However, if you move to such an area, within a few years you are prone to develop allergies to plants and other offenders in the new location.
SOURCE: This information should not substitute for seeking responsible, professional medical care. First created 1995; fully updated 1998; most recently updated 2005.
© Asthma and Allergy Foundation of America (AAFA) Editorial Board