Yellow bile is one of the four humors, which formed the cornerstone of ancient medical practice. It was thought to be one of the four liquids contained within the human body: blood, water, black bile, and yellow bile. Yellow bile was believed to represent the element of fire, and a disproportionate amount of it was thought to cause adverse medical effects and changes in temperament akin to anger.
Humorism was the dominant theory of medical treatment in ancient Greece and Rome as well as in the Islamic world. Medieval Europe inherited this system from the declining Roman Empire and retained it until the 19th century CE. Advances in medicine during this period gave rise to doubts about humorism's validity. By the 1900s, it was considered erroneous.
The development of an organized and cohesive humorist system is largely credited to the ancient Greek physician, Hippocrates, who lived between 460 BCE and 370 BCE. The ideas themselves may have come from ancient Mesopotamia or even Egypt, with many scholars crediting the Egyptian physician, Imhotep. Hippocrates adopted a hands-off approach to medicine, believing that the body's components, or humors, could balance themselves out if nature was allowed to take its course.
Each of the humors is associated with one of the four elements and one of the four temperaments. Yellow bile, also called ichor, represents the hot and dry constituent of the human body and was commonly believed to embody the element of fire. It was believed that the human body must be composed of all four elements found in nature.
An excess of any one humor was thought to produce changes in temperament. Yellow bile was associated with the choleric, or angry, temperament. An unhealthy amount of yellow bile within the body was thought to cause diseases that provoked those affected to behave in such a manner. It was associated with the summer season, and too much exposure to the summer climate was thought to cause an imbalance among the humors, resulting in a choleric disease.
Advances in medicine have revealed that bile is produced by the liver and used for digestion in vertebrates. It is not affected by hot and dry climates, as ancient physicians theorized. The name of the infectious disease cholera is taken from the term choler, another word for yellow bile. Cholera is an infection of the small intestine, where bile aids in digestion, that can lead to dehydration.