How did the four-humors theory explain health and illness in ancient Greece?

In ancient Greece, the theory of the four humors provided a foundational framework for understanding human health and temperament. This concept, which emerged from the work of philosophers like Empedocles and physicians such as Hippocrates, posited that the body was composed of four distinct fluids: blood, phlegm, yellow bile, and black bile.12

Health was defined as a state of equilibrium, where these four humors existed in perfect harmony. Conversely, illness was believed to result from an imbalance or excess of one or more of these fluids. Each humor was associated with specific elemental qualities—hot, cold, wet, or dry—and linked to particular personality traits or temperaments:123

• Blood: Associated with a sanguine temperament (optimistic and enthusiastic).2
• Phlegm: Associated with a phlegmatic temperament (calm and unemotional).23
• Yellow Bile: Associated with a choleric temperament (irritable and angry).2
• Black Bile: Associated with a melancholic temperament (gloomy).42

Later, the physician Galen expanded this theory by suggesting that humoral imbalances could be localized within specific organs, allowing for more precise medical diagnoses and targeted treatments to restore the body's natural balance.5