Smokers have an increased risk of developing the chronic skin condition psoriasis, and that appears to be true both for people who currently smoke as well as past smokers, according to a US study.
The findings, based on a study of thousands of people and published in the American Journal of Epidemiology, do not prove that smoking causes psoriasis in some people -- but it is clear the smoking came before the skin condition, said senior researcher Abrar Qureshi.
“I think if there's one message, it's that for now, smoking seems to be a risk factor for new-onset psoriasis,” added Qureshi, at the Harvard Medical School and Brigham and Women's Hospital in Boston.
Experts believe psoriasis is caused by an abnormal immune system attack on the body's own cells, and some studies have suggested that smokers are more vulnerable, possibly because smoking can affect immune activity.
But most research has looked at people only at one point in time, which makes it hard to be sure the smoking came before the psoriasis.
For the current study, researchers used data from three large, long-running studies of U.S. health professionals, following nearly 186,000 men and women for 12 to 20 years. Of those, 2,410 developed psoriasis during that time.
People who were current smokers at the study's start were almost twice as likely as lifelong non-smokers to develop psoriasis. Past smokers had a 39 percent higher risk than non-smokers.
Past studies have found links between psoriasis and both obesity and heavy drinking, but even after accounting for those factors, the smoking-psoriasis link remained, Qureshi told Reuters Health.
Other studies have pointed to some reasons that smoking could contribute to psoriasis, mainly due to its effects on immune system activity and inflammation. Smokers, for instance, tend to have higher levels of “autoantibodies” -- immune defenses that are mistakenly aimed at the body's own cells.
About 7.5 million people in the United States have psoriasis, according to the National Psoriasis Foundation.
Type 1 psoriasis arises in teenagers and young adults, and is strongly related to family history of the disease, while type 2 arises later in life and tends to be milder.
Qureshi said the current findings don't speak directly to whether quitting smoking will help people who already have psoriasis.
But since psoriasis patients have been shown to have an increased risk of heart disease, and smoking is a major risk factor for heart disease, quitting smoking seems especially important for them, Qureshi added.
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