The severity of the allergic reaction to pollen varies from person to person according to:

  • the immune system of the sensitized person which reacts in different degrees to the allergen
  • the type of pollen to which the person is allergic
  • the intensity of the pollen season.

How is an allergic reaction triggered?

The flowering of plants (trees, grasses and other herbaceous plants) release their allergising pollen grains into the atmosphere between January and September and these can irritate the respiratory tract (nose, throat, bronchial tubes) and the eyes.

The allergy is triggered when:

  • the pollen present in the air enters into contact with the respiratory tract and the eyes
  • on contact with the pollen, the immune system of the sensitized person may react in an excessive way and release histamine
  • inflammation causes dilation of the blood vessels and increases secretions: the nose runs, the eyes become watery and sting.

DID YOU KNOW? The numerous seed parachutes carried by the wind are not pollen but the hairs of the seeds and fruit of plants such as poplars, willows, dandelions, etc. These parachutes are not allergising!

Which pollens are allergising?

The air that we breathe in Belgium transports the pollen of over 40 species of various plants. Fortunately, not all these species are allergising.

For pollen to be allergising:

  • it must contain allergising substances
  • it must be light and small
  • it must be present in large quantities in the air.

Birch, grasses and artemisia (mugwort) are the principal plants with allergising pollen in Belgium.

When are the different pollens released?

The onset, duration and intensity of the pollen season vary every year and depend on weather conditions and the physiological cycles of the plants.

It generally starts in January with the hazel and ends in September with mugwort, with variable intensity and rhythm.

There are 2 different periods in the pollen season:

  • from January to April: trees
  • from May to September: herbaceous plants (grasses, plantain, sorrel, mugwort etc.).

On the advice of your doctor, you can draw up a treatment schedule to protect you during the most critical periods.

Factors promoting the concentration of pollen in the air

Weather conditions affect the presence of pollen in the air:

  • an early spring favours the early appearance of pollen
  • a hard winter slows down the appearance of pollen
  • dry periods favour pollen dispersal by the wind
  • in wet periods pollen is driven down to the ground.

If weather conditions are favourable, there can be several thousands of pollen grains per m³ of air.

The Belgian aerobiological surveillance network “Airallergy” quickly informs general practitioners, specialists, pharmaceutical firms and the general population of the presence of allergens in the air.

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