After an intense pollen season from alder and hazel trees, the birch pollen season has now begun, according to AirAllergy, the national aerobiological monitoring network of federal health institute Sciensano.
The health institute notes that the longer and more intense blooming periods of hazel, alder, and birch – all from the same birch family – make it increasingly difficult for allergy sufferers to remain symptom-free.
Last weekend marked the start of the birch pollen season. In Brussels, concentrations nearly reached 40 birch pollen grains per cubic metre of air.
"We expect daily concentrations to rise further in the coming days, especially with favourable weather conditions," said Astha Tiwari, a scientific collaborator at Sciensano’s Mycology and Aerobiology service. "Once the critical threshold of 80 birch pollen grains per cubic metre is exceeded, most allergy sufferers are at risk of developing symptoms."
This year, the alder pollen season began slightly later than usual, while the birch pollen season started earlier.
According to AirAllergy, this fits into a long-term trend of shifting and increasingly overlapping blooming periods for hazel, alder, and birch trees. If this trend continues, there may be no break between the different blooming phases, leading to a nearly continuous pollen season.
Birch trees are among the most allergenic in Belgium, largely due to the vast quantities of pollen they release. Clinical symptoms of pollen allergies include itchy, watery, and red eyes, sneezing, a blocked nose, congested sinuses, a runny nose, breathing difficulties, loss of taste and smell, and itching at the back of the mouth or in the throat.
To stay informed about the evolution of the hay fever season in Belgium, you can visit the website airallergy.be, use the AirAllergy mobile application, or follow AirAllergy on Bluesky.
