Psoriasis resource center
There’s no question that some people are genetically predisposed to developing psoriasis. According to the National Psoriasis Foundation, at least 10% of the general population inherits one or more of the genetic variants that leads to a vulnerability to the disease.
But other exposures and factors are also associated with psoriasis and may play some causative role. Here is a list of some of them:
Smoking. A meta-analysis and review published in the British Journal of Dermatology in 2014 found an association between psoriasis and both current and past smoking. The larger analysis included three incidence studies that together point to heavier smokers having a greater risk for psoriasis than those with a lighter smoking habit, a finding that is suggestive of a dose effect and a solid clue that there is a cause-and-effect relationship between smoking and psoriasis. Harvard researchers reported results along the same lines in 2012. Using data from the Nurses’ Health studies and the Health Professionals’ Follow-up Study, they found that the risk of psoriasis increased with the number of pack years.
Obesity. Higher levels of inflammatory cytokines, particularly TNF-alpha, in people who are heavy may explain the association between psoriasis and obesity.
Medications. Studies have linked lithium, antimalarial medications, and beta blockers to psoriasis, especially to instances of the worsening of existing psoriasis. Psoriasis can also be a rebound effect of ending treatment with corticosteroids. The National Psoriasis Foundation says Inderal—a brand-name version of propranolol—makes the disease worse in about 25%–30% of patients with psoriasis.
Infections. Viral and bacterial infections may worsen psoriasis.
Alcohol. About a third of people with moderate-to-severe cases of psoriasis drink excessively, and some research has shown a direct relationship between alcohol intake and the size of the area of the skin that is affected. Researchers at the University of Manchester in England reported findings in JAMA Dermatology last year that showed that alcohol-related mortality was higher among people with psoriasis than among those without it (4.8 deaths per 10,000 person years vs. 2.5 per 10,000 person years). The main cause of the alcohol-related deaths is alcoholic liver disease, according to this report. Alcohol may have a deadly effect because people who drink heavily are less likely to stick with psoriasis treatments. It may also increase the liver toxicity of methotrexate.
Vitamin D. The research into the relationship between vitamin D levels and psoriasis is one of those epidemiologic mixed bags, with some studies finding an association and others not finding one. Even when a study finds an association, the direction of the cause and the effect is hard, if not impossible, to sort out. People with psoriasis may wind up having low vitamin D levels because they avoid sunlight and have decreased UV exposure rather than low vitamin D levels contributing in some causal way to the psoriasis.
Stress. Stress is commonly linked to psoriasis—and to both onset of new cases as well as to flare-ups of existing ones. Some reviews of the research have found, though, the evidence of the association underwhelming.
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