From Arsenic to Biologicals: A 200 year History of Psoriasis is a chronological description of how the unravelling of the mechanisms underlying psoriasis have led to a change from the empirical "try it and see" treatments of the 19th and early 20th centuries to the evidence-based treatments of the present day. The book explains the various theories proposed to explain psoriasis and describes the introduction of new treatments, decade by decade, throughout the 20th century. These range from the belief that psoriasis resulted from an internal metabolic disturbance in the 19th century, when arsenic was the systemic treatment of choice, through to the 21st century when the recognition that psoriasis is a disease of the immune system enabled the development and use of therapeutic biological agents.