Research Article: Association of co-exposure to extreme cold and nitrogen dioxide with psoriasis outpatient visits and systemic inflammation
Abstract:
Psoriasis, a chronic inflammatory skin disorder, is closely linked to environmental triggers. However, the combined effects of extreme cold and nitrogen dioxide (NO 2 ), two common environmental factors, on psoriasis patients remain unclear. This study aims to explore the associations of co-exposures to extreme cold and NO 2 with psoriasis outpatient visits and systemic inflammatory markers among patients with complete blood count (CBC).
Data from patients with psoriasis were collected in a subtropical megacity of China between January 2021 and December 2025. A distributed lag non-linear model (DLNM) was used to evaluate the outpatient visit risk associated with extreme cold, extreme NO 2 , and their co-exposure, identifying susceptible subgroups. Additive interaction was assessed using an interaction term and the relative excess risk due to interaction (RERI). Furthermore, to evaluate the effect of co-exposure on systemic inflammatory markers, a sub-cohort of patients with CBC records was extracted for exploratory analysis.
A total of 63,411 psoriasis outpatient visits and 3,048 patients who underwent CBC tests were recorded during the cold seasons of 2021–2025. Co-exposure to extreme cold and NO 2 was associated with an increased risk of psoriasis outpatient visits at Lag14 (RR?=?1.017, 95% CI: 1.004–1.030), with a higher point estimate compared to single-factor exposure; however, the interaction test was not significant (RERI?=?0.026, 95% CI: ?0.055 to 0.108). Stratified analysis revealed that the association between co-exposure and outpatient visits varied by age, with a stronger effect observed in younger age groups (Q-test for interaction, p =?0.004). In exploratory analyses, SII showed a significant global association ( p =?0.016) at Lag7 (OR?=?1.109, 95% CI: 1.031–1.194), whereas NLR and PLR were not significant.
Co - exposure to extreme cold and NO 2 is associated with an increased risk of psoriasis outpatient visits, particularly in susceptible age groups, although no synergistic effect was detected between the two exposures. Exploratory analyses also suggest a potential association with elevated systemic inflammation, warranting further investigation. These findings provide preliminary evidence for the role of combined environmental exposures in psoriasis and highlight the importance of considering age-specific vulnerability when developing targeted public health interventions for at-risk populations.
Introduction:
Psoriasis, a chronic inflammatory skin disorder, is closely linked to environmental triggers. However, the combined effects of extreme cold and nitrogen dioxide (NO 2 ), two common environmental factors, on psoriasis patients remain unclear. This study aims to explore the associations of co-exposures to extreme cold and NO 2 with psoriasis outpatient visits and systemic inflammatory markers among patients with complete blood count (CBC).
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