The study shows the risk of psoriasis was 78% higher among current smokers compared with people who had never smoked and 37% higher among smokers who had quit previously.
"These findings, along with well-established hazardous health effects of smoking, provide clear incentives for smoking cessation in those at risk for and suffering from psoriasis," writes researcher Hyon K. Choi, MD, DrPH, of Harvard Medical School, and colleagues in the American Journal of Medicine.
Smoking Linked to Psoriasis
Researchers looked at the relationship between smoking and psoriasis in more than 78,500 female registered nurses who took part in the Nurses Health Study II. The women were followed for 14 years, and during that period 887 cases of psoriasis were reported.
Researchers measured lifetime smoking exposure in pack-years. A pack-year is the number of packs smoked per day multiplied by the number of years a person has smoked.
The results showed that smoking not only increased the risk of psoriasis, but heavier smoking increased that risk further. For example, compared with women who never smoked, the risk of psoriasis was 60% higher for those with a smoking history of 11-20 pack-years and more than two times high for those with 21 or more pack-years of smoking.
Researchers found the risk of psoriasis decreased after quitting smoking, with the risk of psoriasis among former smokers comparable to nonsmokers 20 years after quitting.