Smoking and the risk of psoriasis in women: Nurses' Health Study II.

BACKGROUND

Psoriasis is a common, chronic, inflammatory skin disorder. Smoking may increase the risk of psoriasis, but no prospective data are available on this relation.

METHODS

We prospectively examined over a 14-year time period (1991-2005) the relation between smoking status, duration, intensity, cessation, and exposure to secondhand smoke, and incident psoriasis in 78,532 women from the Nurses Health Study II. The primary outcome was incident, self-reported, physician-diagnosed psoriasis.

RESULTS

We documented 887 incident cases of psoriasis. Compared with those who had never smoked, the multivariate relative risk (RR) of psoriasis was 1.78 (95% confidence interval [CI], 1.46 to 2.16) for current smokers and 1.37 (95% CI, 1.17 to 1.59) for past smokers. Compared with nonsmokers, the multivariate RR of psoriasis was 1.60 (95% CI, 1.31 to 1.97) for those who had smoked 11-20 pack-years and 2.05 (95% CI, 1.66 to 2.53) for those who had smoked > or =21 pack-years. Compared with never smokers, the multivariate RR of psoriasis was 1.61 (95% CI, 1.30 to 2.00) for those who quit smoking <10 years ago, 1.31 (95% CI, 1.05 to 1.64) for 10-19 years ago, and 1.15 (95% CI, 0.88 to 1.51) for > or =20 years ago. Prenatal and childhood exposure to passive smoke was associated with an increased risk of psoriasis.

CONCLUSIONS

In this prospective analysis, current and past smoking, and cumulative measures of smoking were associated with the incidence of psoriasis. The risk of incident psoriasis among former smokers decreases nearly to that of never smokers 20 years after cessation.