Human proneness to anger, or irritability, has – from the earliest writings on physical health – represented a disturbance in physiological function and manifested itself as a disturbance of mood. Since antiquity, irritability has been associated with a range and variety of irascible verbal and physical behaviours. Yet, for the most part, the literature on irritability lies buried and forgotten. Our current conceptualization of irritability, a symptom present in a variety of mental and physical conditions, might be traced to the "disease model" of mental illness prevalent in medicine in the late 19th and early 20th centuries.