The historical impact of the four humors medical theory

For over a millennium, Western medicine was based on the theory of the four humors, a system that attributed health and disease to the balance of four bodily fluids: blood, phlegm, yellow bile, and black bile.

Attributed to the Hippocratic tradition and later systematized by Galen, this framework sought natural and observable causes for illness rather than supernatural explanations. Galen expanded the theory by linking these humors to qualities such as heat, cold, dryness, and moisture, suggesting that diet, sleep, and environmental factors influenced a patient's health. While modern science has since debunked the biological basis of this theory, it served as a foundational medical standard for centuries.