A case-control study investigated the possible association between psoriasis and viral hepatitis. The study included 12,502 patients aged > 20 years and 24,287 age- and gender-matched controls. The prevalence of hepatitis C was significantly increased in the patients (1.03 vs. 0.56%; P < 0.001). An interaction with smoking was noted (odds ratio [OR]: 1.93 for smokers and OR: 2.27 for nonsmokers); however there was no significant difference between smokers and nonsmokers in the multivariate model. While hepatitis B prevalence was higher in patients than controls (0.74% vs. 0.56%; P = 0.043), this relationship was not robust in a multivariate model (P = 0.15) (Cohen, A.D. et al. Dermatology 2010, 220: 218).