Pollen is one of the most frequent causes of allergy.
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Allergens > Airborne allergens
| > In the outdoor air |
| > Pollens |
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Pollens
Which are the pollens causing allergy?
When told that they are allergic to pollen most people automatically picture in their mind bright coloured and strong smelling flowers with stamina heavily covered with a thick layer of yellow pollen (such as a water lily). Contrary to the general belief, pollen of these plants is generally innocuous and a very, very rare cause of allergy.
To understand which is the pollen that can cause allergy, you have to know what pollen is and what his role is.
Pollen is formed from very small (microscopic) granules which represents the male semen of the flowering plants. Plant fertilization implies transport of the pollen granules from one flower to another. There are two main ways in which pollen transport occurs:
- Carried by insects or birds. Insect pollinated plants have attractive flowers, vividly coloured and with strong perfume to attract the carriers. The pollen grains are big (in microscopic terms), heavy and sticky and consequently cannot float in the air for long periods of time. This pollen can cause allergy only in exceptional circumstances (for ex. in people working in green houses which spend many hours daily in close contact with these flowers).
- Carried by the wind. Wind pollinated plants have small, hardly noticeable flowers and produce very large amounts of pollen which is released in the air and transported by the wind for miles and miles away. As seems normal these pollen particles are small and very light and dry so they can float in the air for a very long time. This is the allergenic pollen that causes problems in the allergy sufferers.
Which are the plants producing allergenic pollen?
The main sources of allergenic pollen are: grasses, trees and weeds.
Grasses are the most frequent cause of pollen allergy worldwide. The grasses most frequently related to pollen allergy are: Timothy grass, Rye grass, cocksfoot, Bermuda grass, orchard grass, Kentucky grass,
Trees: The most common allergenic species include: silver birch, hazel, alder, poplar, olive, cypress, oak, chestnut, elm, maple, walnut.
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| Fig. 1 Tree pollen grains seen through the scanning electron microscope: Alder pollen (A), Birch pollen (B), Hazel pollen (C), Olive pollen (D).(Courtesy of Louis De Vos, Free University of Brussels) |
Weeds and shrubs: From this category of plants
Ragweed produces probably the most aggressive pollen which is the
main cause of pollen allergy in North America and is becoming an
increasingly problem in Europe. Other allergenic weeds include:
mugwort, goosefoot, wall pellitory, plantain, and weeds from the
Compositae family etc.
Different types of allergenic plants will be found in different parts of the world.
Different types of allergenic plants will be found in different parts of the world.
Tip: moving to a place where the plant producing the pollen you are
allergic to does not grow is not a solution for your disease. Most
often, after a variable time interval (which can take up to a few
years) you will develop symptoms to the pollen present in the new
area.
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| Fig. 2 Predominance of allergenic pollens in different region across the world. |