Effect of smoking cessation on psoriasis vulgaris, palmoplantar pustulosis and generalized pustular psoriasis

BACKGROUND: Smoking is a known risk factor for psoriasis; however, the impact of smoking cessation on psoriasis has seldom been evaluated. OBJECTIVES: We aimed to examine the effects of smoking cessation on the development of psoriasis vulgaris (PsV), palmoplantar pustulosis (PPP) and generalized pustular psoriasis (GPP). METHODS: Using the Korean National Health Insurance Service database, we retrospectively compiled a cohort of 5 784 973 participants without psoriasis, analysed their changes in smoking status from 2004 to 2007 and followed up new cases of psoriasis until 2021. The psoriasis risks were compared with those of sustained smokers, smoking quitters, sustained ex-smokers and never smokers using multivariate Cox proportional hazard models. RESULTS: The mean age of the participants was 47.1 years (SD 13.5) and 3 092 426 (53.5%) were male. During 77 990 688 person-years, 67 364 psoriasis cases were identified. Compared with sustained smokers, smoking quitters showed a reduced risk of developing psoriasis [adjusted hazard ratio (aHR) 0.91; 95% confidence interval (CI) 0.87-0.95], specifically PsV (aHR 0.92; 95% CI 0.88-0.97) and PPP (aHR 0.71; 95% CI 0.63-0.79). The reduction in risk due to smoking cessation was more prominent in sustained ex-smokers (psoriasis: aHR 0.77, 95% CI 0.74-0.79; PsV: aHR 0.76, 95% CI 0.73-0.79; PPP: aHR 0.56, 95% CI 0.51-0.61; GPP: aHR 0.64; 95% CI 0.52-0.78). When conducting sensitivity analyses to address the potential for changes in smoking habits after 2007, the results and trends were consistent with the main findings, and a more pronounced significance was observed. CONCLUSIONS: Compared with continuous smoking, smoking cessation was associated with a decreased risk of developing psoriasis. The risk-reducing effect of smoking cessation was more pronounced in those maintaining a smoke-free status. Smoking cessation and the maintenance of a smoke-free status should be encouraged to prevent the development of psoriasis and all other smoking-related diseases.