Birch trees are currently in full bloom.
On Thursday, 109 birch pollen grains per m³ of air were measured in Brussels.
Airborne pollen amounts may vary depending on weather conditions. During dry and sunny spells, concentration can be high.
People allergic to birch pollen should remain cautious and follow the treatment prescribed by their doctor.
Ash, hornbeam, poplar and willow are also in flower.