Abstract

Psoriasis is a chronic, immune-mediated inflammatory skin disease affecting approximately 125 million people worldwide. Once considered a simple disorder of skin cell overgrowth, we now understand it as a complex systemic disease driven by dysregulated immune responses, genetic susceptibility, and environmental triggers. This book synthesises the current state of scientific knowledge on psoriasis, drawing on peer-reviewed literature spanning immunology, genetics, epidemiology, and therapeutics. We present the molecular and cellular mechanisms of disease pathogenesis, including the central IL-23/IL-17 axis (explained fully in Section 6), in terms accessible to readers without prior immunology training. We also review the genetic architecture of psoriasis susceptibility, environmental risk factors, associated comorbidities, and the revolution in targeted biologic therapies that has transformed patient outcomes over the past two decades.