Cigarette smoking, body mass index, and stressful life events as risk factors for psoriasis: Results from an Italian case-control study

We conducted a case-control study to analyse the association of psoriasis of recent onset with smoking habits, body mass index (BMI) and stressful life events. Cases (n = 560; median age 38) were patients with a first diagnosis of psoriasis and a history of skin manifestations of no longer than two years after the reported disease onset. Patients with a new diagnosis of skin diseases other than psoriasis (n = 690; median age 36) were selected as controls. The risk of psoriasis was higher in ex- and current smokers than in never-smokers, the relative risk estimates (OR) being 1.9 for ex-smokers and 1.7 for smokers. Smoking was strongly associated with pustular lesions (32 patients, OR = 5.3 for smokers). The frequency of psoriasis varied significantly in relation to a family history of psoriasis in first degree relatives, BMI (OR = 1.6 and 1.9 for over weighted, BMI 26-29, and obese, BMI ≥ 30, respectively) and stressful life event score (compared to the lower index quartile, the OR being 2.2 for index values ≥ 115). Risk estimates, when taking into consideration the combined effect of these factors with smoking habits, were consistent with a multiplicative model of risk combination with no significant statistical interaction.