Vigorous exercise, like running or aerobics, has been shown to lower the risk of developing psoriasis by as much as 30 percent, according to Harvard researchers.

Previous studies have linked people who are overweight and smokers to an increased risk of developing psoriasis, a common skin condition that causes itchy, reddish, and painful plaques.

A study, published in the journal Archives of Dermatology, found that women who report spending more than one hour per week running or four hours per week doing aerobics were 25 to 30 percent less likely to develop the chronic skin disease, compared to women who didn't.

Researchers said the findings held true even after the women's weight and other lifestyle habits were taken into account.

"What we don't know for sure at this stage is whether losing weight and exercising vigorously will prevent you from getting psoriasis," Dr. Joel Gelfand, a dermatologist from the University of Pennsylvania Perelman School of Medicine in Philadelphia, who wasn't involved in the new study, told Reuters Health.

"But these are all things that are good to do anyway and have multiple proven benefits beyond their effect on the skin," he said, recommending that people at risk of psoriasis, including those with a family history of the condition, step up their exercise routine.

However, researchers noted that not all exercises reduced the likelihood of developing the painful skin condition.

"Among the individual vigorous activities we evaluated, only running and performing aerobic exercise or calisthenics were associated with a reduced risk of psoriasis," the researchers wrote in the study. "Other vigorous activities, including jogging, playing tennis, swimming and bicycling were not associated with psoriasis risk. The highly variable intensity at which these activities are performed may account for this finding."

The study consisted of 86,665 women who were part of a larger Nurses' Health Study II. Researchers said that at the beginning of the study, none of the women had psoriasis, and they were followed up on their physical activity levels in 1991, 1997 and 2001.

Throughout the study period, researchers found that 1,026 of the women had developed psoriasis.

They also found that women who were the most active also had the lowest risk of developing the skin condition.

"In addition to providing other health benefits, participation in vigorous exercise may represent a new preventive measure for women at high risk of developing psoriasis," the authors wrote. "Additional corroborative studies and further investigations into the mechanisms by which physical activity protects against new-onset psoriasis are needed."

The skin condition is very common, and can happen to anyone. It commonly begins between the ages of 5 and 35, and it is not contagious.

The National Institutes of Health predicts that nearly 2.6 percent of the U.S. population has psoriasis, and 15 percent of those people may also have psoriatic arthritis.

Previous studies have also linked exercise to a lower chance of on diseases marked by systemic inflammation, including type 2 diabetes, colon cancer, coronary artery disease, and breast cancer.