HealthDay News — Smoking is an independent risk factor for psoriasis, with particularly strong associations for heavy smokers and those who have smoked for many years, study results indicate.

Past and current smokers were more likely to develop incident psoriasis compared with never smokers (relative risk = 1.39 and 1.94, respectively), and this risk increased with the number of cigarettes smoked, Wenging Li, PhD, from Harvard Medical School in Boston, and colleagues reported in the American Journal of Epidemiology.

They analyzed data from 2,410 adults with incident psoriasis who were identified among 185,836 participants in three studies, including a cohort of older women  from the  Nurses’ Health Study, 1996–2008, a cohort of younger women from the Nurses’ Health Study II, 1991–2005, and a cohort of men from the Health Professionals’ Follow-up Study, 1986–2006.

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Among current smokers, the researchers determined the relative risk for incident psoriasis increased as cigarettes smoked per day went up. The relative risk for those who smoked one to 14 cigarettes was 1.81, compared with 2.04 among those who smoked 15 to 24 cigarettes, and 2.29 among those who smoked 25 or more per day.

Similarly, there was a trend toward an increased risk for psoriasis as the number of pack-years or duration of smoking increased. The highest risk was identified among those with 65 or more pack-years of smoking (RR=2.72) and for those with a smoking duration of 30 or more years (RR=1.99). Conversely, the risk of psoriasis was reduced with increasing time since the participant stopped smoking.

“Although it has important public health indications, there is [a] lack of awareness of the association between smoking and psoriasis. We provide further evidence showing that smoking is an independent risk factor for the development of psoriasis among U.S. women and men,” the researchers wrote.

Li W et al. Am J Epidemiol. 2012;175(5):402-413.