Meteorological and environmental factors that impact pollen counts, allergenicity, and thresholds: A scoping review

Background: Pollen is a key source of aeroallergens responsible for allergic rhinitis, conjunctivitis, and asthma. Objective: The goal of this scoping review was to summarize current available literature on the factors that affect pollen counts, allergenicity, and thresholds that induce symptoms in individuals who were sensitized. Methods: Several databases showed no published articles with a similar scope as of January 2022. A search of these data bases yielded 373 articles for assessment. These were then reviewed for relevance, and articles were selected to demonstrate the breadth of available data on pollen counts, allergenicity, and thresholds that induce symptoms in individuals who were sensitized. Additional articles were identified through examination of bibliographies of search-identified articles. Results: Several environmental factors have shown a correlation with pollen counts and allergen load, including the distance from the source, wind characteristics, pollen size, terrain, urban environments, air composition (particulate matter, CO₂ levels, ozone, NO₂), and weather conditions (humidity, thunderstorms, precipitation). Pollen thresholds at which symptoms were induced varied by study, pollen type, symptom, disease, and location. In addition, there was heterogeneity in study designs, threshold definition, and outcome measures. Conclusion: This scoping review demonstrates the plethora of variables that influence the relationship between pollen and the symptoms of allergic diseases. Analysis of the available data sheds light on the complex interaction between environmental and biologic factors that affect pollen's role in allergic diseases and provides guidance on multiple areas for further investigation.