The following is a summary of “Ambient pollen exposure and pollen allergy symptom severity in the EPOCHAL study,” published in the April 2024 issue of Allergy & Immunology by Luyten, et al.

Ambient pollen exposure triggers nasal, ocular, and pulmonary symptoms in individuals with allergies, yet the detailed shape of the exposure-response relationship still needs to be explored. For a study, researchers sought to characterize the association by investigating whether symptom severity varies among different subpopulations, how the exposure-response relationship evolves throughout the pollen season, and which time lags in pollen exposure are most relevant to symptom development.

In the study, 396 adult participants with allergy symptoms were asked to repeatedly score the severity of their nasal, ocular, and pulmonary symptoms, aggregating into three composite symptom scores. Individual hourly pollen exposures to seven allergenic plants (alder, ash, birch, hazel, grasses, mugwort, and ragweed) were calculated, considering personal sensitization and exposure time lags up to 96 hours. Generalized additive mixed models with a random personal intercept were used to analyze the data, adjusting for weather conditions and air pollution as potential time-varying confounders.

The analysis revealed a clear nonlinear positive association between pollen exposure and the severity of ocular and nasal symptoms among individuals with pollen allergies. Specifically, symptom severity increased sharply with initial increases in pollen exposure but plateaued and attenuated beyond approximately 80 pollen grains per cubic meter. No threshold for symptom onset was identified, indicating that symptoms can occur at any level of exposure. Recent pollen exposure, particularly within the last 5 hours, had the most significant impact on symptoms, but effects persisted for up to 60 hours. Additionally, exposure to grass pollen (as opposed to tree pollen) and a younger age group (18–30 years) were associated with greater nasal and ocular symptoms severity.

The study’s findings suggested that there is no distinct threshold for pollen exposure below which symptoms do not occur, and the dose-response relationship exhibits attenuation at higher exposure levels. These insights may inform future revisions of pollen warning systems to incorporate multi-day pollen concentration data to better manage and predict allergic symptoms throughout the pollen season.

Reference: onlinelibrary.wiley.com/doi/10.1111/all.16130