Allergic rhinitis takes a heavy toll in Belgium. Pollen is an important trigger but fungal spores might also influence the onset of symptoms. The purpose of this study was to assess the health impact of these aeroallergens based on their repercussion on allergy medication sales in the Brussels-Capital Region. Methods: The relationship between daily changes in pollen and spore concentrations and daily changes in reimbursable systemic antihistamine sales has been investigated with times series analysis. 8 pollen and 2 spore species were tested for different age and gender categories. A generalized linear model was used and adjusted for air pollutant concentrations, climate factors, flu, seasonal component and day of the week. Analysis focused on the 2005-2011 period. Results: For most age groups, the relative risk of buying allergy medications associated with an interquartile augmentation in pollen concentrations increased significantly for Betula, Carpinus and Gramineae. Associations existed but were less consistent across ages for Quercus, Fraxinus, and Taxus Cupressaceae. Considering a 10 days cumulative effect, the relative risk reached up to 1,11 (95%CI [1,09-1,12]) for Gramineae among the 19-39 years customers. Risk pattern varied according to gender. Discussion: Little research in this field has been carried out worldwide and extrapolation from previous studies is hazardous given the high influence of the local context. This multidisciplinary study is the first of this kind in Belgium and demonstrates the large health consequences of Gramineae and several common tree species for the Brussels area. It distinguishes itself by its duration, sensitivity and completeness of data (any sale of reimbursable drugs was captured, daily data of various cofactors were used). This work opens several research perspectives related to subpopulation sensitivity or impact of climate modification (changes in pollen concentration, occurrence of novel aeroallergens).