You're overweight

People with psoriasis who are obese in their teens may be more likely to get psoriatic arthritis, according to a 2010 study in the Archives of Dermatology. 

Fat tissue may promote more circulating cytokines, the cell-signaling molecules linked to inflammation. In that study, body mass index (BMI) at age 18—but not current BMI—was linked to risk.

A previous study by the same group suggested current weight might, in fact, play a role. Still, more research is needed to prove the link.