MILAN—If risk of lung cancer, cardiovascular disease, and chronic hacking coughs are not enough to convince your patients to quit smoking, maybe the threat of psoriasis will do the trick.

Cigarette smokers have a 2-fold increased risk for developing psoriasis, according to data from US and European studies over the last decade. Women appear to be at greater risk than men, said Dr. Luigi Naldi, at the seventh International Psoriasis Symposium.

Dr. Naldi, of the dermatology clinic, Ospedali Riuniti, Bergamo, Italy, found that individuals who smoke more than a pack a day (20 cigarettes or more) have a 2.2-fold increased lifetime odds ratio for psoriasis. Fifteen to 24 cigarettes carries an odds ratio of 1.7. Under 15 butts a day, the odds ratio is 1.4.

“There is a clear dose-response pattern,” said Dr. Naldi, adding that in his tobacco-loving country, 40% of all individuals with psoriasis are current smokers.

The findings came from a study by the Italian Group for Epidemiologic Research in Dermatology, comparing life-long smoking histories in 396 psoriatic patients and 432 healthy controls. The data showed a definite gender difference.

Women who smoked more than 15 cigarettes daily had a psoriasis odds ratio of 3.2, as compared to 1.6 for men with equivalent habits. The reason for this apparent difference is not clear.

The Italian group is not the first to report a smoking-psoriasis association. In 1991, dermatologists at the Mayo Clinic, Rochester, Minn., found 40.3% of psoriatics in their dermatology service were current smokers, as compared to only 28% of the general Minnesota population at the time.

Norwegian researchers compared 106 psoriasis patients with 106 controls, and found that 46% of the psoriatics were current smokers; 24.5% were huffing one or more packs per day. Among the controls, only 23.6% were smokers, with 6.6% smoking a pack or more daily. Boiling it down, the investigators concluded that a 20-butt daily habit confers a psoriasis odds ratio of 5.3.

The smoking-psoriasis connection may explain an observation by British epidemiologists that the odds ratio for lung cancer is 2.3 fold higher among men with psoriasis compared with the general British population. In women with psoriasis, the odds ratio is increased to 3.7.

Cigarettes are a cornucopia of pro-psoriatic chemicals. Dr. Naldi said there are more than 4,000 substances in cigarette smoke that can modulate immune function. Keratinocytes, the key players in psoriasis, have surface receptors for nicotine.

The apparent link between tobacco use and psoriasis is compelling, but further research is needed to determine if smoking is truly an etiologic factor, or merely a reflection of patients’ emotional stress.

Smoking and drinking are common playmates. So, what about alcohol? Increased consumption also seems to correlate with psoriasis, though the link is not as strong, said Dr. Naldi. The Norwegian investigators found that a daily intake of greater than 100 grams of alcohol per day increased the odds of psoriasis by a factor of 2.2.

In the Italian cohort Dr. Naldi estimated that three to four drinks confers a psoriasis odds ratio of 1.6, and that five or more give an odds ratio of 1.5. If alcohol does increase psoriasis risk, it doesn’t appear to do so in a dose-dependent manner.

Interestingly, alcohol seems to affect men more than women. Males who down three or more alcoholic drinks per day have a 1.8 odds ratio for psoriasis, as compared to 1.1 among females with similar consumption levels.

The role of lifestyle factors in the etiology of psoriasis remains somewhat controversial, and demands far more study. But Dr. Naldi stressed that the observed patterns are consistent across four countries, and at least for smoking, there is a biochemical rationale for positing increased risk. “In principle, these associations have big public health implication.”

THE REDUX: Epidemiologic studies in Europe and the US suggest that cigarette smokers are at two to five-fold greater risk for psoriasis compared with non-smokers; the risk is more pronounced in men.