General Information - Pollen
Pollen grains are microscopic or small reproductive structures produced in the anthers, or male elements, of seed bearing plants. They are dispersed mainly by air, water or animals.
Plants with colourful flowers are generally insect pollinated or entemophilous and do not get airborne in large numbers, or at all. Trees, shrubs and weeds that depend on the wind for pollination are called anemophilous and generally do not produce large colourful fragrant flowers.
Aerobiology Research laboratories is concerned with airborne pollen that contain allergens causing health problems such as allergies and asthma. Examples of important aeroallergens are oak, birch, maple and ragweed. We do, however, observe some pollen from insect pollinated plants or trees on our samples, but they are usually in low numbers and do not play an important role in allergic reactions.
When pollen from anemophilous plants become airborne they can be carried for long distances. The chemical makeup of pollen is the basic factor that determines whether it is likely to cause an allergic reaction. The size of the particles can also influence the kind of reaction that may occur. Large pollen grains do not tend to travel deep into the lungs or alveoli and therefore more often cause allergic reactions and not asthma. If particles or fragments, which tend to be smaller, become airborne and end up deep in the lungs they can cause an asthmatic reaction. Other species, like pine trees for example, can produce large amounts of pollen but their chemical makeup is such that it rarely causes allergic reactions.
Weeds can produce copious amounts of pollen in the air. Ragweed is the major culprit, but others such as sagebrush, pigweed, English plantain and Russian Thistle can also be significant allergens.
Grasses and trees are also important sources of allergenic pollen. Some of the most prevalent trees that produce allergic reactions include oak, ash, elm, hickory, pecan, box elder, the birch family and mountain cedar (found in some parts of the United States), although other tree pollen have been known to cause allergic reactions in some individuals. Some species of trees, such as the cottonwoods, shed a residue commonly called "June snow". Although this residue is often mistaken for pollen, it is not and does not carry the antigen that is present in the pollen. However, it does often contain fungi such as Cladosporium sp., and can elicit allergic reactions from those sensitive to these fungal spores.
Only a few species of the grass family are considered highly allergenic, but the vast quantity of grass pollen released each year means that grasses are considered a significant allergen in many locations. Grass allergies are somewhat of a special case, as the allergen is also introduced into the air when the grass is mowed. As such, people are being primed to the antigen of the plant long before grass pollen is released, and allergic reactions are often elicited before significant pollen counts are observed.
Flowering plants such as roses and tulips are unlikely to cause allergies in humans unless individuals are sensitized through prolonged close contact. Most people do not have enough direct contact with pollen grains of flowering plants to become sensitized.
Pollen allergies are seasonal in nature. The start, duration, and yield of a tree-pollinating season can vary drastically from year to year. This depends on the type of winter and spring, and weather conditions during pollination. The start of a season can vary by as much as a month from year to year for certain trees, and daily fluctuations in temperature, rain and sun exposure can also affect the amount of pollen released on a daily basis. Grasses and weeds such as ragweed occur during the summer and as such are less affected by winter and spring temperatures.
Pollen reports are usually a measure of how much pollen is in the air. They often give a measure of the total concentration of pollen with little indication of the types of pollen found or the portion that is made up of allergenic species. A more meaningful and informative report is one that includes a breakdown of specific types of pollen that may cause allergic reactions and their relative concentrations. Using these species-specific reports, asthma and allergy sufferers may be able to identify their own unique sensitivities and thus monitor the levels of allergens in the air that are relevant to them.
The information presented here is designed to inform, not replace, the relationship that exists between a patient and a medical professional.