In the spring months, the pollen of hazel, alder and birch cause hay fever and pollen asthma and determine the severity of the allergic symptoms. Since 2018, hazelnut pollen has been appearing in rising concentrations throughout Germany – this was also the case in 2022. Alder pollen has diminished slightly in 2022, after sweeping through Germany at unprecedented levels in 2021 and 2019.
Birch pollen, along with grass pollen, are the most common types of pollen that cause hay fever, asthma and intolerance to pome and stone fruits (oral allergy syndrome). In 2022, there was an increase in birch pollen levels compared to previous years. Overall, therefore, 2022 was a pronounced “tree pollen year”. Beech, oak, pine and spruce also released large amounts of pollen compared to previous years, although pollen from pine and spruce does not cause allergies.
Grass pollen concentrations have been rising steadily since 2019 and reached a new peak in 2022. These pollens have been shown to cause inflammation of the mucous membranes in the respiratory tract. Pollen triggers the production of IgE antibodies in affected individuals, who are then considered “sensitised” and thus become more prone to developing hay fever and pollen asthma. Interestingly, people in big cities become sensitised to tree and grass pollen more often than those living in small towns or villages.
A new study has now shown  that air pollutants – and in particular particulates and nitrogen oxides – chemically alter the allergens in birch pollen, causing the allergens to become even more allergenic. The higher rate of sensitisation to pollen in air-polluted environments can therefore be seen as a consequence of both the effect of air pollutants on plants and their pollen, but also of increased hypersensitivity of mucous membranes of people living in cities.
In addition to increased allergenicity of pollen, inflammation of the mucous membranes due to air pollutants also changes, causing those affected to have increased symptoms of itching of the nose and eyes, reddening of the eyes, runny nose and asthma symptoms.
 Stawoska I., Myszkowska D., Oliwa J., Skoczowski A., Wesełucha-Birczyńska A., Saja-Garbarz D., Ziemianin M. Air pollution in the places of Betula pendula growth and development changes the physicochemical properties and the main allergen content of its pollen. PLoS One. 2023 Jan 25;18(1):e0279826