Weather

Pollen allergy and hay fever

All the information about pollen allergy and hay fever that is published on our website is provided by the Belgian Aerobiological Surveillance Network, which is managed by the Mycology & Aerobiology service from Sciensano.

The main allergenic pollens in Belgium

As soon as the first pollen grains appear again in the air, the dates of beginning and end of the season will be updated.

AllergenBeginning of the seasonEnd of the season
Alder06 February 201915 March 2019
Ash20 March 201928 April 2019
Birch16 March 201903 May 2019
Grasses17 May 201930 July 2019
Hazel06 February 201915 March 2019
Mugwort23 July 201928 August 2019
Oak10 April 201921 May 2019

The grass pollen

In Belgium, the grass pollen season usually last from May 15th to July 15th.

During this period, we evaluate the daily risk to develop hay fever symptoms by taking into account the measured airborne pollen concentrations (pollen grains/m³) and the weather forecast.

The risk index can be: 

  • Null: No grass pollen grain is expected in the air. Consecutive days with this index usually announce the end of the grass pollen season.
  • Low: Low grass pollen concentrations in the air are expected but may be sufficient to cause allergic symptoms in highly susceptible individuals. The usual eviction measures are already recommended.
  • High: High grass pollen concentrations in the air are expected. Many individuals allergic to this pollen are susceptible to feel symptoms. The usual eviction measures are recommended.
  • Very high: Very high grass pollen concentrations in the air are expected. Most of the individuals allergic to this pollen are susceptible to feel symptoms. It is strongly recommended to avoid any activity outside.

We also measure the timing variations of the risk periods every year for the other main allergenic pollens.

For more information on the allergenic pollens, please visit the website www.airallergy.be of Sciensano.