Pollen Allergen

The Pollen FAQ

Frequently asked questions regarding pollen and pollen allergenicity. Please choose a question from the list below, or scroll down to read our answers.

What is pollen?
Pollen grains are small and cannot be seen by the naked eye. Sometimes trees release so much pollen in the air that a cloud of pollen can actually be seen. Pollen grains are the male reproductive bodies of plants (like the sperm of animals) by which the female flowers are fertilized. This is how the plant reproduces and keeps the species alive. (top)

How is pollen collected?
There are different types of technologies or methods used to collect pollen from the air. The most commonly used is a simple technology where a small plastic rod, coated with grease, rotates in the air and the pollen sticks to it as it spins. (top)

How does one count pollen?
The small plastic collecting rods are stained and placed on a microscope, so one can see the pollen, count and identify them. (top)

How does one obtain a count for allergens that are in outdoor air?
A greased rod is spun in the air at regular intervals for 24 hours. When the rod is removed the laboratory counts the number of pollen grains on the rod. A known volume of air has been sampled and the count is reported in grains per cubic meter of air. This number is used to give an indication of whether or not the concentration of certain pollen is low or high. This should help Doctors and allergy sufferers, who follow allergy reports, to know which pollen are in the air and what the concentration is. (top)

Is pollen from certain trees, flowers or weeds more allergenic than others?
The simplest answer is yes. Pollen that get airborne are of more concern than those that are insect pollinated. Airborne pollen are the ones that cause allergies because they can be inhaled. Insect pollinated ones, such as from flowers, are not of much concern. Flowers are only a problem to highly sensitized individuals who are exposed by touching the plant and perhaps inhaling lots of pollen from their hands. Often what people are reacting to when it comes to decorative flowers and plants is the scent and not the pollen. It is also important to note that pollen from certain trees and weeds and grasses are more allergenic than others. Box-elder (a species of maple) is highly allergenic, whereas the pollen from poplar is less so. Ragweed is one of the most highly allergenic plants. (top)

Do all plants that produce pollen cause allergic reactions?
No. The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants (trees, grasses and weeds). The showy plants that produce colourful flowers are insect pollinated and usually do not get airborne. Pollen from plants which are wind pollinated, however, are not all allergenic. The protein found in certain plants that are wind-pollinated are what a person's immune system is reacting to. This protein is not only found in the pollen but also in plants parts that get airborne. This is why someone who has allergies to grass reacts when they walk on a freshly cut lawn. (top)

Why are some pollen allergenic while others are only minor allergens or do not cause allergic reactions at all?
The chemical makeup, or protein, of pollen is the factor that determines whether it is likely to cause allergic reactions. (top)

I have allergies, why are they worse some years than others?
The seasons for trees, weeds and grasses are very different from year to year. This is largely due to the effect of weather and the environmental stresses on determining how much pollen will be produced and is released from year to year. An example is if we have a very cold wet spring when the trees are pollinating it ca have an impact on the amount of pollen found in the air. This will somtimes cause a short pollen season with low pollen levels. Another example is if we have a very dry spring and summer than the amount of grass pollen in the air will be lower since the plant biologically goes dormant if it does not have enough water. If the grass is not growing it also will not have as much pollen to release. (top)

What is the significance of pollen counts?
Pollen counts are important as they give vital information as to what is in the air. Allergists and their patients can compare what is actually in the air and the allergy symptoms and evaluate the effectiveness of treatment programs. (top)

How can I avoid pollen when I have allergies?
The simplest thing is to avoid being outdoors as much as possible when the particular plant you are allergic to is flowering. Air conditioners and filters are also very helpful. Antihistamines and an effective treatment program with an allergist can help in relieving some of the symptoms. (top)

I see pollen from cottonwood trees on the ground in June, why are you not predicting any pollen counts?
The Cottonwoods are a species of Populus, and by June their pollen season will have been long over. What we see in June in many parts of the country is what some people refer to as "June snow." This is a residue left over from the seed production process -- when the seed pods open they release cotton-like tufts of fluff which create the illusion of snow on the ground. This material does not contain any pollen. However, it can contain high levels of fungal spores such as Cladosporium sp., which can cause allergic reactions in people sensitive to fungal spores. (top)

I am allergic to grasses, and my allergies are here now but the grass pollen levels in your reports are low -- is this a mistake or a data error?
Grass allergies are a bit of a special case in aerobiology, because pollen release is not the only way that grass allergens are introduced into the air. The allergen is found throughout the plant, including both the blades of grass as well as the pollen, and as such the allergen is introduced into the air whenever grass is mowed. This means that people allergic to grasses are being subjected or "primed" to the antigen long before we see grass pollen in the air, and many people have allergic reactions before we report significant pollen counts. (top)


The information presented here is designed to inform, not replace, the relationship that exists between a patient and a medical professional.

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