Validation of the Pollen Resilience Index as an integrated pollen–pollution–heat stress indicator for allergic rhinitis symptoms

Environmental exposure assessments lack integrated indicators capable of accounting for the simultaneous impact of biological and chemical stressors. To address this, we developed the Pollen Resilience Index (PRI), an integrative indicator designed to measure the combined burden of allergenic pollen, air pollutants, and heat stress. The index incorporates hourly concentrations of four pollen taxa ( Alnus , Betula , Poaceae, and Artemisia ), five pollutants (PM 10 , NO 2 , O 3 , SO 2 , and CO), and a Humidex index calculated from forecasted temperature and relative humidity. Each input was quantised into five levels; an hourly PRI was then calculated using a max-pooling rule, and hourly values were aggregated into daily classes to facilitate comparison with health-related records. PRI was assessed using anonymised symptom diaries from Patient Hay Fever Diary users. Across moderate conditions (PRI 2–4), symptom reports appeared broadly stable, whereas more pronounced changes were observed under environmental extremes. At PRI 5, 53.0% of users reported nose symptoms (compared with 38.3% at PRI 4), and 32.1% reported eye symptoms (compared with 23.4%). Under more favourable conditions (PRI 1), symptom prevalence was lower (eye symptoms 14.2% vs. 24.5% at PRI 2). Results suggest that the PRI is a compact and scalable tool that effectively captures both symptom escalation and relief, providing a practical means to complement traditional air-quality indicators and enhance health communication. The PRI model is open access and can be downscaled and tailored to selected territories and specific user needs. • PRI integrates pollen, pollutants, and weather into a single hourly index. • PRI uses max pooling of 10 inputs and aggregates into daily index classes. • Symptom prevalence increased with load level, strongest for nasal and ocular symptoms. • Nasal symptoms increased from 38.3% at PRI4 to 53.0% at PRI5 • Ocular symptoms fell on PRI1 days (14.2%) but rose sharply at PRI5 (32.1%).