In the world of diseases, psoriatic arthritis is a double-edged sword. On one end you have the inflammation, joint pain, stiffness, and swelling that comes courtesy of arthritis. On the other end are the hallmark red, itchy, scaly patches of skin that psoriasis brings (consider yourself doubly blessed). According to the National Psoriasis Foundation, psoriatic arthritis affects about one million people in the United States. Most people with the disease develop psoriasis first and arthritis later. And it doesn’t take much for one disease to turn into the other—especially in the way of the psoriasis. “When I think someone has psoriatic arthritis, I'll go on a rash hunt, and a lot of times, the only thing I’ll find is a little patch of psoriasis behind the ears,” says Martin Bergman, M.D., chief of the division of rheumatology at Taylor Hospital in Ridley Park, PA and clinical professor of medicine at Drexel University College of Medicine.