Psoriasis is an autoimmune disease that causes severe itchiness and irritation. It affects about 2 to 3 percent of the population. This disorder causes the skin's cells to proliferate, growing at a too-rapid rate. As a result, these excess skin cells form dry, red skin patches that are thick and scaly. In this video, dermatologist Keith Choate, MD, explains what psoriasis is and how biologics are helping patients cope.