Smoking history increases psoriasis risk in women.

Women who smoke cigarettes increase their risk of developing psoriasis by 78%, according to a large prospective, longitudinal study.

The increased risk appears to be dose dependent, wrote Dr. Arathi R. Setty of Harvard Medical School, Boston, and colleagues. The greatest risk occurred among women with a history of at least 21 pack-years of smoking. Those women more than doubled their risk of developing psoriasis. Women with a history of 11-20 pack-years incurred a 60% increase in risk and those with a history of 1-10 pack-years had a 20% increase in risk compared with women who never smoked.

These statistically significant results are adjusted for age, body mass index, and alcohol intake (Am. J. Med. 2007;120:953-9).

The study involved 79,628 female registered nurses enrolled in the Nurses Health Study II. The investigators excluded 1,096 women with a history of psoriasis at baseline. In 1991, when the study began, the average age of the women was 35.5 years and the average BMI was 24.5 kg/[m.sup.2].

At baseline, 66% of the women reported never having smoked, 23% reported being former smokers, and 11% reported being current smokers.

During 14 years of follow-up, the investigators documented 887 incident cases of psoriasis for an overall incidence of 1.1%. Overall, 56% of the cases occurred among women who had never smoked.

Current smokers who reported smoking at least 25 cigarettes per day were 2.5 times more likely to develop psoriasis than were those who never smoked. Past smokers who had smoked for at least 20 years were 57% more likely to develop psoriasis than were those who had never smoked.

Women who quit less than 10 years previously had a 61% elevated risk compared with women who never smoked, those who quit 10-19 years previously had a 31% elevated risk, and those who quit 20 or more years previously showed no statistically significant increase in risk.

Exposure to passive smoke was an additional significant risk factor for developing psoriasis. Women whose mothers smoked while pregnant with them had a 21% increased risk, compared with women with no prenatal exposure. Women who were exposed to passive smoke as children had an 18% increase in risk, but women who were exposed as adults had no significant increase in risk.

BY ROBERT FINN

San Francisco Bureau