What was the relationship between humours and illnesses?

The ancient medical system of humoralism, which originated in ancient Greece, held that the human body consisted of four essential fluids or "humours": blood, phlegm, yellow bile, and black bile. Each humour was associated with a specific temperament and a set of physical characteristics. An imbalance of humours was believed to lead to illness, while maintaining a balance of humours was seen as essential for good health.

According to humoralism, each of the four humours was associated with a specific element and quality:

- Blood (sanguine): hot and wet, associated with the element of air

- Phlegm (phlegmatic): cold and wet, associated with the element of water

- Yellow bile (choleric): hot and dry, associated with the element of fire

- Black bile (melancholic): cold and dry, associated with the element of earth

An excess of any one humour was thought to cause specific physical and emotional symptoms. For example:

- Too much blood could lead to a ruddy complexion, a tendency to rashness and anger, and a risk of diseases such as apoplexy and epilepsy.

- Too much phlegm could cause paleness, lethargy, and a susceptibility to colds and other respiratory illnesses.

- Too much yellow bile could result in a yellowish skin tone, irritability, and a propensity for inflammatory conditions such as fevers and jaundice.

- Too much black bile could cause a dark complexion, depression, and a predisposition to chronic diseases such as cancer and melancholia.

To restore balance and promote healing, physicians would often prescribe treatments aimed at reducing the amount of the offending humour. These treatments could include bloodletting, purging, vomiting, and the administration of herbs and other natural remedies.