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Media Resources: Pollen Q&A

What is pollen?
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.

What is a pollen count?
Pollen counts measure the amount of airborne allergens present in the air. Counts are compiled by a variety of methods. Pollen counts 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.

How do you acquire pollen counts?
The American Academy of Allergy, Asthma and Immunology has a network of pollen counters across the United States. Each counter works under the direction of an AAAAI member and must first pass an intensive certification course. Counters use air sampling equipment to capture air-borne pollens. The number of pollen grains collected are then counted and logged.

How is a pollen count interpreted?
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.

Can weather affect a pollen count?
Weather can influence hay fever symptoms. Allergy symptoms are often minimal on days that are rainy, cloudy or windless, because pollen does not move about during these conditions. Hot, dry and windy weather signals greater pollen and mold distribution and therefore, increased allergy symptoms.

If you are allergic to plants in your area, you may think that moving to another area of the country with different plants will lessen your symptoms. However, many pollens (especially grasses) and molds are common to most plant zones in the United States. Additionally, other related plants can also trigger the same symptoms. Many people who move to a new region to escape their allergies find that they acquire allergies to new airborne allergens prevalent in their area within one to two years. Therefore, moving to another part of the country to escape allergies is often ultimately disappointing, and not recommended.

Why is there a disparity between two counting stations in the same city?
There are a number of reasons that could explain the difference, including the time of day that the sample was taken a change in temperature, wind conditions, humidity or precipitation; or differences in surrounding geography.

The time of day that aeroallergens are sampled can account for variances in the amount of pollen measured. Pollen concentrations are usually highest after the dew dries after sunrise to late morning. If one station samples at 8 a.m. and the other station samples at 2 p.m., there could be a significant difference in pollen concentration.

Weather conditions also affect pollen levels. The most variant factors influencing different pollen counts from approximately the same region are wind, humidity, and the proximity of the sampling equipment to pollen producing vegetation.

Because pollens are small, light and dry, they can be easily spread by wind, which keeps pollen airborne and carries it over long distances. If one station samples when the wind is strong and the other station samples when the wind is calm, there's bound to be a difference in the pollen levels.

When the air is humid, such as during or after it rains, pollen becomes damp and heavy with moisture, keeping it still and on the ground. If one station samples right before a rain storm, and the other station samples just after it rains, there will probably be a significant difference in the concentration of pollen.

Another reason to account for the difference is the proximity of the sampling equipment to pollen producing vegetation. Samples taken from an urban area, where there is little vegetation, will most likely differ from samples taken from a rural area, where there is more vegetation.

Is the pollen season the same from year to year?
The beginning and ending times of tree, grass and weed pollen seasons are very similar from year to year in the same location. Intensity differs every year based on the previous year's weather, current weather, and other environmental factors.

If a station is several miles from my home, will the counts apply to my area?
It's difficult to provide accurate pollen and spore levels for areas not near a pollen counting station. If the climate and geography are similar, chances are the figures reported by the station are a good indicator of conditions nearby.

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