Pollen is the vehicle for the male gamete of plants, and needs to be
transported to the female gamete in order to fertilize it, and consequently,
in order to ensure the survival of the plant species.
With this aim, plants mainly use two strategies, in accordance with which
plants can be classified:
Entomophils (from the Greek Entomos= insect) è
these plants reproduce themselves by means of insects. These usually
have very eye-catching and beautiful flowers in order to attract
insects, and so their pollen is normally quite sticky. When a insect
alights on a flower to suck the nectar, pollen sticks to the hair on its
legs. Then, when the insect goes to another flower, some of this pollen
sticks and thus fertilises the plant.
Anemophils (from the Greek Anemos = wind) è
these plants reproduce themselves by means of the wind. They do not have
beautiful flowers, because they do not need to attract insects. So, they
usually have small pollen, that comes off very easily and in great
quantities when the wind blows, and is carried by the wind great
distances ("aero-roaming"), thus permitting the fertilisation
of other plants of the same species.
Several plants have a mixed form of fertilization (anemophil and
From this point, and taking into account that people become allergic by
breathing pollen floating in the wind, it is easy to infer a series of very
From an allergologic point of view the most important are Anemophil
plants, because their pollen will be present in the air in very high
quantities, and consequently the more anemophils, the more allergologic.
So, pollen from plants with beautiful flowers (Entomophils such as
roses, carnations, etc.) do not normally produce allergy, because their
pollen does not travel in the air so easily.
The most common symptoms in people allergic to pollen are respiratory
symptoms, because airways are the ways through which the person enters
into contact with pollen: Conjunctivitis (itchy eyes, tears,…),
Rhinitis (sneezing, nasal obstruction, itchy nose,…), and lower airway
symptoms (cough, asthma,…). Sometimes wheals and swelling can also
Generally speaking, spring and summer is usually the worst time of the
year for people allergic to pollen, because this is when plants normally
pollinate, although it is neither exclusive to this season nor
inevitable, depending as it does on the kind of plant responsible for
the pollen that causes the allergy.
Windy days are the worst for people allergic to pollen because this is
when anemophil plants give off the greatest quantities of pollen to the
atmosphere. In coastal areas, days when the wind blows from inland
(i.e.: west wind in eastern coasts, north wind in southern coasts,
People allergic to pollen usually improve during rainy weather because
rain helps to "clean" the atmosphere.
It is probable that a patient allergic to pollen will become worse
when he/she is in a geographical area where they are many plants to
whose pollen he/she is allergic. However, this does not guarantee that
when the patient is far away from these areas, that he/she will be free
from problems, because pollen can be transported by the wind many dozens
There is no generic allergy "to pollen", and allergy to
pollen is specific to each plant: for example, there are people allergic
to olive tree pollen who tolerate birch pollen perfectly well; people
allergic to grass pollen who tolerate cypress pollen, etc. So, for an
appropriate treatment, it is absolutely essential to diagnose which type
of pollen is responsible for the patient's problem in order to establish
a specific treatment.
The specific treatment for pollen allergy is Vaccination. It has been
clearly demonstrated that this treatment is highly effective for
controlling patients allergic to pollen, provided that the pollen
responsible for the patient's symptoms has been properly diagnosed, and
a high quality Vaccine is administrated regularly, and over an adequate
period of time.
BRIEF DESCRIPTION OF A POLLEN GRAIN
Pollen grains are microscopical structures, commonly with a diameter of
10 to 60 microns (µm), and usually round or ovoid, inside which the
reproductive material is located. In order to protect such material, pollen
is covered by two protective membranes: one external (the EXINE), the
other internal and thinner (the INTINE).
Neither the Intine nor the Exine are insurmountable barriers, because
they must allow the passage of the genetic material when the plant is
fertilised. This occurs through PORES, or through elongated furrows,
called COLPI. Depending on the number of Pores a pollen has, it can
be classified as Monoporated, Biporated, Triporated, Multiporated, etc. If
pollen has Colpi, it will be Monocolpated, Bicolpated, Tricolpated, etc.
Pollen frequently have both Pores and Colpi, and in this case they will be
"Colporated" (Monocolporated, Bicolporated, etc.). Some pollens
apparently have neither Pores nor Colpi, and then they are
"un-aperturated". All these things help us to differentiate
between different kinds of pollen with a microscope.
Furthermore, Exine (the outer surface) can have very different surface
textures, and it is very easy to dye it. This also helps to distinguish
pollens with a microscope:
There are many other textures, such as smooth, striated, perforated,
The size of the pollen also helps to differentiate them. Depending on the
size, they can be classified as:
< 10 µm
10 - 25 µm
25 - 50 µm
50 - 100 µm
100 - 200 µm
> 200 µm
We can collect pollen with special machines (see picture). This collector
has a weathercock that orientates the nozzle to the direction of the wind.
It also has a vacuum pump, that aspirates a constant flow of air through the
nozzle. In this way, pollen impacts against a plastic ribbon soaked in
silicone and placed on a cylinder that makes one complete revolution every
The ribbon is changed every week, and is divided in segments
corresponding to the days of the week. Every fragment is put on a glass
plate, then it will be dyed, and so we can see it with a microscope,
identify and count pollens. In this way, we can not only count the
concentration of each type of pollen in the air (counted in grains of pollen
per cubic metre of air), but also know the day and even the time of these
In "The most allergenic pollens" pages we will have a look at a brief
explanation of the most important characteristics of some of the significant
plants in Europe from an allergologic point of view, and of their pollens.
You can also see similarities and differences between them. Additionally,
you will be able to see the months and regions in Europe with higher levels
of pollen for each group of plants.