Vigorous physical activity may be associated with a reduced risk of psoriasis, scaling of the skin, U.S. researchers suggest. Hillary C. Frankel of Brigham and Women\'s Hospital in Boston said psoriasis is an immunologic disorder characterized by systemic inflammation and scaling of the skin. Frankel and colleagues used data from the Nurses\' Health Study II -- involving 86,665 women who did not have psoriasis at baseline in 1991 and who completed physical activity questionnaires in 1991, 1997 and 2001. Researchers documented 1,026 incident cases of psoriasis. \"Our results suggest that participation in at least 20.9 metabolic equivalent task hours per week of vigorous exercise, the equivalent of 105 minutes of running or 180 minutes of swimming or playing tennis, is associated with a 25 percent to 30 percent reduced risk of psoriasis compared with not participating in any vigorous exercise,\" the study authors said in a statement. The findings are published online in the Archives of Dermatology.