Impact of Seasonal, Environmental, and Inflammatory Factors on Chronic Urticaria Activity and Serum Biomarkers: A Prospective Cohort Study

<b>Background:</b> Chronic urticaria (CU) is characterized by recurrent wheals and/or angioedema persisting for more than six weeks. While disease triggers are often unidentified, seasonal and environmental factors may modulate disease activity; however, evidence regarding their clinical impact remains limited. <b>Objective:</b> This study aimed to evaluate the effects of seasonal, meteorological, and pollutant-specific environmental factors on urticaria control using the Urticaria Control Test (UCT), and to compare these effects between chronic spontaneous urticaria (CSU) and chronic inducible urticaria (CIU) in relation to inflammatory serum biomarkers. <b>Materials and Methods:</b> This prospective observational study was conducted at the Allergy and Clinical Immunology outpatient clinic of Kirikkale University Faculty of Medicine between 1 June 2023 and 1 April 2024. Patients with CU were classified as CSU or CIU according to international guidelines. Each participant was evaluated during summer and winter seasons. Area-level air pollution data and meteorological parameters were obtained from national monitoring systems. Disease control was assessed using the UCT, and inflammatory biomarkers were analyzed. <b>Results:</b> Urticaria control showed significant seasonal variation, with lower UCT scores during summer and higher scores during winter in both CSU and CIU patients. Among environmental factors, ozone (O₃) was the only pollutant consistently associated with poorer urticaria control, whereas particulate matter and traffic-related pollutants, despite being higher in winter, showed no clinically relevant association. Summer months were characterized by increased inflammatory activity, including elevated leukocyte counts, neutrophil-to-lymphocyte ratio (NLR), C-reactive protein (CRP), and D-dimer levels, particularly in CSU patients. D-dimer emerged as an independent marker associated with poor disease control during summer. <b>Conclusions:</b> CU demonstrates marked seasonal variation, with disease worsening during summer months. Pollutant-specific effects, particularly O₃ exposure, rather than overall air pollution burden, appear to be clinically relevant in urticaria control. Inflammatory and coagulation-related biomarkers may provide additional insight into disease activity. These findings support a season-aware and individualized management approach and highlight the need for future studies incorporating individual-level exposure assessment and biomarker-guided strategies.