Supplementary Material for: Association between Polycyclic Aromatic Hydrocarbon Metabolites and Psoriasis in US Adults: Evidence from the National Health and Nutrition Examination Survey

Background: Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants with widespread human exposure and have been associated with adverse health outcomes. However, their potential relationship with psoriasis remains insufficiently explored.
Objective: The aim of this study is to investigate the association between PAH exposure and psoriasis.
Methods: Data were obtained from the National Health and Nutrition Examination Survey (NHANES) for the periods 2005–2006, 2009–2010, and 2011–2012. Weighted multivariate logistic regression analysis was performed to assess the association between individual PAH metabolites and psoriasis. Bayesian kernel machine regression (BKMR), quantile g-computation (qgcomp), and weighted quantile sum (WQS) regression were used to evaluate the relationship between mixed PAH exposure and psoriasis, as well as to determine the relative contributions of specific PAH metabolites. Stratified and sensitivity analyses were conducted to assess result stability.
Results: A total of 4,912 participants (mean age, 43.52 years; 95% CI, 42.65–44.39 years) were included, of whom 2,514 (51.18%) were female, and 141 (2.87%) were diagnosed with psoriasis. Multivariate logistic regression analysis identified significant positive associations between psoriasis and seven urinary PAH metabolites: 2-hydroxynaphthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, 3-hydroxyphenanthrene, 1-hydroxyphenanthrene, 2-hydroxyphenanthrene, and 1-hydroxypyrene. Analysis of mixed exposure PAH across all three models demonstrated significant positive associations between urinary PAH metabolites and psoriasis, with 2-hydroxyphenanthrene and 2-hydroxynaphthalene identified as primary contributors. Stratified and sensitivity analyses confirmed the robustness of these results, and the observed associations persisted among non-smokers.
Conclusion: Both single and mixed exposure analyses demonstrated a positive association between PAH exposure and psoriasis. These findings suggest that reducing PAH exposure may help mitigate psoriasis risk.