According to the National Psoriasis Foundation, psoriasis is a chronic, autoimmune disease that appears on the skin. It occurs when the immune system sends out faulty signals that speed up the growth cycle of skin cells. Psoriasis is the most prevalent autoimmune disease in the United States, affecting as many as 7.5 million people, or 2.2 percent of the U.S. population, with associated costs of $11.25 billion annually. According to the World Psoriasis Day consortium, as many as 125 million people worldwide (2 to 3 percent of the Earth’s population) have psoriasis.