<p><i>Betula pendula</i> is a short-lived tree that is often planted in urban environments due to its rapid growth and low ecological requirements. However, the Bet v 1 protein contained in its pollen is one of the main allergens in such environments, with a high variation in allergen content among individual trees. We investigated the factors driving variation in allergen content in individual birch trees in Bratislava and its surroundings. Bet v 1 levels in the pollen samples collected from 98 trees were determined by ELISA and statistically correlated with site- and tree-specific variables. We found that distance to the nearest water body and building shade were the strongest environmental predictors of pollen allergen content: greater distance from water bodies was associated with lower allergen content, while building shade was associated with higher allergen content. Other important parameters included building coverage in the area around the trunk, distance from the nearest road and building, and fungal infection. Significant variation in Bet v 1 concentrations was observed between urban and peri-urban/rural areas, with some differences among urban districts. The identified environmental parameters provide information about stress factors that cannot be directly measured for each tree, the most important being drought and heat/radiation stress. The findings are significant for the management of urban green spaces, highlighting the need for an individualised approach to reducing the allergenic potential of urban green zones.</p>