BOSTON, Massachusetts—Women who smoke increase their risk of developing psoriasis, heavy smokers increase it more, and the risk does not revert to normal until 20 years after a woman stops smoking, according to investigators from Massachusetts General Hospital, Brigham and Women's Hospital, and Harvard School of Public Health, all in Boston, USA; and from Vancouver General Hospital, in British Columbia, Canada.

The investigators, led by Arathi R. Setty, MD, MPH, of the Massachusetts General Hospital, report  in the November 2007 issue of The American Journal of Medicine that the relative risk for psoriasis was 37% higher among past women smokers than among women who had never smoked and 78% higher among current smokers.

"In our cohort, 14% of the incident psoriasis cases were attributable to having ever smoked. For past smokers, 27% of the risk was attributable to smoking; for current smokers, 44% of the risk was attributable to smoking," Dr. Setty wrote.

Psoriasis risk increased with amount of smoking. Compared with women who never smoked, the risk was 20% higher for 1 to 10 pack-years, 60% higher for 11 to 20 pack-years, and more than two times higher for >21 pack-years. (One pack-year is equivalent to smoking 20 cigarettes per day for 1 year). This trend was observed in both current and past smokers.

"The current study provides the first prospective evidence that smoking is a strong risk factor for incident psoriasis," Dr. Setty noted.

Exposure to passive smoke in utero or during childhood also was associated with an increased risk of psoriasis. Adjusted for body mass index, alcohol consumption, and self-smoking status, the age-adjusted relative risk for psoriasis was 1.21 for offspring whose mothers smoked while pregnant, 1.18 for offspring exposed to passive smoking as a child, and 1.10 for those exposed to passive smoke after age 18.

This study is the largest prospective assessment of multiple markers of smoking status, duration, and intensity in relation to the risk of psoriasis. The researchers analyzed data from the Nurses Health Study II, an ongoing longitudinal study of 116,608 female registered nurses from 15 states between the ages of 25 and 42 at baseline who completed and returned an initial questionnaire in 1989. This population had 887 incident cases of psoriasis during the 14 years of follow-up.

The investigators suggest that "smoking cessation may be a potentially important for the prevention and management of psoriasis."

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