Even During Pollen Season, Being Outside in Nature Can Benefit People Allergic to Birch Pollen

Birch Tree Pollen

Birch Tree Pollen

During the pollen season, many people with allergies tend to avoid nature. That isn’t entirely justified, a new KU Leuven study into biodiversity and health suggests. People allergic to birch pollen experience fewer symptoms after being exposed to certain natural environments, such as pastures and forests. An important condition is that the environment shouldn’t be dominated by allergenic tree species, and that there are no high concentrations of pollen or air pollution.

When temperatures rise in spring, many people seek out the outdoors. Especially during the current pandemic, social life takes place mostly outside. This poses a dilemma for those who suffer from pollen allergies: go out into nature and confront the dreaded pollen, or stay indoors? In the RespirIT project, researchers from KU Leuven sought to find a solution in collaboration with colleagues from UHasselt, UNamur, Sciensano (the Belgian Institute of Health), and the Royal Meteorological Institute of Belgium.

Using a smartphone app, the researchers registered the whereabouts of 144 Belgian adults with a birch pollen allergy. They followed the participants during the birch pollen seasons (January to May) of 2017 and 2018. Each evening, the participants indicated in the app which allergy symptoms they had experienced that day.

Exposure to nature

“We analyzed which environments the participants were exposed to and on which days they did or didn’t have severe allergy symptoms,” explains Michiel Stas of KU Leuven, whose PhD research was part of the RespirIT project. “We noticed that severe symptoms were linked to high concentrations of pollen and air pollution. These symptoms even occurred one or two days after the exposure took place. Rather unexpectedly, we also noticed that after being exposed to pastures and forests, the participants experienced no or only mild symptoms.

“We can conclude that people with a birch pollen allergy don’t necessarily have to avoid nature altogether during the pollen season. An important condition is that the environment they seek out is not dominated by allergenic tree species, such as alder, hazel, or birch.”

Poor air quality worsens symptoms

The study indicates that next to allergenic tree species and their pollen, air quality is also a crucial factor in the development of allergy symptoms. “Air pollution harms the respiratory system, which makes people more sensitive to pollen,” promotor Ben Somers adds. “It also causes trees to produce pollen that contain more allergens and as such can lead to more severe allergic reactions.”

“More nature and greener cities can contribute to an improvement to our daily environment. It is, however, important that such a natural environment is diverse and not dominated by allergenic tree species, so that people with pollen allergies can also enjoy these beneficial effects,” Michiel Stas concludes. “People who are allergic to birch pollen definitely do not have to lock themselves up during the pollen season, but should think strategically about the right time and place for a refreshing walk. The weather forecast or Sciensano’s website AirAllergy can be of help.”

Reference: “Exposure to green space and pollen allergy symptom severity: A case-crossover study in Belgium” by Michiel Stas, Raf Aerts, Marijke Hendrickx, Andy Delcloo, Nicolas Dendoncker, Sebastien Dujardin, Catherine Linard, Tim Nawrot, An Van Nieuwenhuyse, Jean-Marie Aerts, Jos Van Orshoven and Ben Somers, 22 March 2021, Science of The Total Environment.
DOI: 10.1016/j.scitotenv.2021.146682

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