Humorism, also called the humoral theory, was a medical idea that explained how the human body was made and how it worked. This theory was used by doctors and thinkers in Ancient Greece and Rome.

Humorism became less popular in the 17th century and was finally shown to be incorrect when scientists discovered microbes.

Origin

The idea of "humors" may have started in Ancient Egypt or Mesopotamia, but it wasn't fully developed until ancient Greek thinkers. The word "humor" comes from the Greek word chymos, which means "juice" or "sap" and can also mean "flavor." Early Indian Ayurveda medicine described a theory of three or four humors, called doṣas, which were sometimes connected to the five elements: earth, water, fire, air, and space.

The concept of "humors" became more important after the writings of medical theorist Alcmaeon of Croton (around 540–500 BC). His list of humors included elements like water, earth, fire, and air, which were also described by Empedocles. Hippocrates is usually credited with applying the idea of humors to medicine. Unlike Alcmaeon, Hippocrates believed humors were the vital bodily fluids: blood, phlegm, yellow bile, and black bile. Both Alcmaeon and Hippocrates thought that having too much or too little of any humor could cause illness. Hippocrates and later Galen suggested that a small imbalance in these fluids could lead to different behaviors.

A text attributed to Hippocrates, On the Nature of Man, explains that the human body contains blood, phlegm, yellow bile, and black bile. These substances make up a person’s health. Health happens when these substances are in the right amounts and mixed well. Pain occurs when one substance is too much or too little, or when it is not mixed with others. The body relies on the four humors because their balanced combination helps keep people healthy. Having the correct amount of each humor is essential for health. Diseases are caused by too much or too little of a humor.

The On the Nature of Man text and Galen’s later comments on it became the starting point for the tradition of humoral theory. One reason this theory became popular was because Galen was a respected authority.

Even though modern science no longer uses the four humors, the idea that the body has basic substances and structures is still relevant.

Some Hippocratic texts mention the four humors, but others only described two humors, and some avoided discussing the theory altogether. The idea of the four humors remained popular for centuries, largely because of Galen’s writings. According to Hippocrates, the four humors are in balance and help maintain health. Hippocrates linked the four humors to the four elements—earth, fire, water, and air—proposed by Empedocles, but this connection was not made by Hippocrates or Galen, who focused on bodily fluids.

Galen believed that humors were created in the body, not eaten, and that different foods could influence which humors were produced. For example, warm foods might lead to more yellow bile, while cold foods might lead to more phlegm. Seasons, life stages, geography, and jobs also affected the types of humors a person had. For example, cities with hot winds were thought to have more digestive problems due to excess phlegm, while cities with cold winds were linked to lung diseases and other health issues. Cities in the west were believed to produce weak, unhealthy people who were more likely to get sick. A Hippocratic text called On Airs, Waters, and Places describes a doctor testing a city’s wind, water, and soil to predict how these factors might affect the health of its people.

A key idea in Hippocratic medicine was to find the causes of illness in the body’s structure and in environmental factors like air, water, and food. Each humor is made by a different organ and has its own composition. Aristotle’s idea of eucrasia, which means a state of balance, was connected to the four humors and helped shape a more mathematical approach to medicine.

An imbalance of humors, called dyscrasia, was thought to cause all diseases. Health was linked to a balance of humors, or eucrasia. The qualities of the humors influenced the types of diseases they caused. Yellow bile was linked to warm diseases, and phlegm was linked to cold diseases. In On the Temperaments, Galen emphasized the importance of qualities like warm, cold, moist, and dry. He identified four main temperaments, each dominated by one quality, and four more where two qualities combined. These last four—sanguine, choleric, melancholic, and phlegmatic—became well-known. The term "temperament" later referred to personality traits, but Galen used it to describe physical and emotional tendencies that influenced health.

Diseases could also happen

Four humors

The theory of humorism had models with two, three, or five parts, but the most well-known model includes four humors: black bile, yellow bile, phlegm, and blood. These were described by Hippocrates and later expanded by Galen. Each humor was linked to one of the four traditional temperaments. According to Hippocratic medicine, health depended on the balance of these humors in amount and strength. This balance was called eukrasia.

Galen improved the theory by combining his knowledge of humors with ideas from past philosophers. He believed the interactions of humors helped explain how the body works. Galen connected parts of the soul—thumos (spiritedness), epithumos (desire), and Sophia (wisdom)—to the brain, heart, and liver. This idea came from Aristotle’s approach to explaining physical observations. Galen also believed organs (organa) had specific functions (chreiai) that helped maintain the body. These functions were shown through a person’s activities (energeiai). While Galen linked parts of the body to the soul, he focused on how the four humors interacted with natural bodily processes to explain human development.

Galen wrote about the connection between humors and seasons in his work On the Doctrines of Hippocrates and Plato. He said: "Children are like spring, young men like summer, mature men like autumn, and old men like winter." He also linked humors to seasons based on their properties. Blood, which was hot and wet, was connected to spring. Yellow bile, hot and dry, was linked to summer. Black bile, cold and dry, was tied to autumn. Phlegm, cold and wet, was connected to winter.

Galen believed the soul’s traits were influenced by the body’s mixtures but said phlegm did not affect character. In On Hippocrates’ The Nature of Man, he wrote: "Sharpness and intelligence come from yellow bile, perseverance from black bile, and simplicity from blood. Phlegm has no effect on the soul." He also said blood is made of four elements: water, air, fire, and earth.

Modern medicine uses different terms. Today, there is no distinction between black and yellow bile, and phlegm has a different meaning. It was once believed that humors were the basic substances in bodily liquids. In 1921, Swedish doctor Robin Fåhræus suggested the four humors were based on observing blood clotting in a glass container. When blood is left undisturbed, it separates into four layers: a dark clot (black bile), red blood cells (blood), white blood cells (phlegm), and clear yellow serum (yellow bile).

During the golden age of the four humors, many Greek texts were written. One was an anonymous work called On the Constitution of the Universe and of Man, published by J. L. Ideler in the 19th century. It linked the four elements (air, water, earth, fire) to the four humors (blood, yellow bile, black bile, phlegm).

In the 17th century, English playwright Ben Jonson wrote plays where characters were based on their humoral traits.

It was believed that blood provided energy for the body and soul and contained small amounts of the other three humors. Blood samples were used to check the balance of humors. Blood was linked to a sanguine nature (enthusiastic and social) and was hot and wet, like spring.

Yellow bile was connected to a choleric nature (ambitious and short-tempered) and was found in the gallbladder or in bodily fluids like vomit. It was hot and dry, like summer and fire. Too much yellow bile was thought to cause emotional issues like anger.

Black bile was linked to a melancholy nature, a term from Greek for "black bile." Excess black bile was blamed for depression and cancer. It was cold and dry, like autumn. Black bile was seen as harmful and opposite to blood, which was considered the most beneficial.

Phlegm was associated with a phlegmatic nature (reserved behavior) and described bodily secretions like mucus or saliva. It was linked to the brain due to its color and texture. In 1910, French scientist Charles Richet questioned the existence of humorism’s "phlegm" as a real substance. Phlegm was connected to winter because it was cold and wet.

Humor production

Humors were thought to be created during digestion as the final result of liver digestion. Digestion is an ongoing process that happens in all animals and can be broken into four steps: gastric digestion, liver digestion, blood vessel digestion, and tissue digestion. Each step processes food until it is ready for the body to use. During gastric digestion, food is turned into chylous, which the liver can absorb and further process. In the liver digestion stage, chylous becomes chymous. Chymous contains the four humors: blood, phlegm, yellow bile, and black bile. These humors then move through the blood vessels. In the final stage, tissue digestion, food is transformed to resemble the type of tissue it will support in the body.

If any part of the process that creates humors fails, it can cause an imbalance that leads to illness. Healthy organs are needed to produce proper humors. The stomach and liver must work correctly for digestion to proceed normally. If gastric digestion is disrupted, the liver, blood vessels, and tissues do not receive enough chylous, which can lead to abnormal humors and blood composition. A healthy liver cannot change abnormal chylous into normal chylous or proper humors.

Humors are the final result of gastric digestion, but they are not the end of the digestion process. If abnormal humors are created during liver digestion, they can affect other parts of the digestive system.

Relation to jaundice

According to ancient Greek medical theory, jaundice is described in the Hippocratic Corpus. Early records of jaundice (called icterus) come from Hippocratic physicians. The illness is mentioned many times in the Hippocratic Corpus, where details about its causes, appearance, expected outcomes, and treatments are provided. The five types of jaundice listed in the Hippocratic Corpus all involve a yellow or greenish color in the skin.

Today’s doctors may recognize the symptoms of jaundice described in the Hippocratic Corpus as similar to those found in modern medical books. Although the treatments used by Hippocratic physicians are not practiced in modern medicine, their careful observations of different types of jaundice were impressive. The Hippocratic Corpus includes many references to jaundice. At the time, jaundice was considered a separate illness, not a symptom caused by another disease.

Unification with Empedocles's model

Empedocles believed there were four elements: earth, fire, water, and air. He thought the earth helped form natural systems. Because this idea was widely accepted for many years, later scholars matched qualities linked to each humor, as described by Hippocrates and Galen, with seasons and "basic elements" as explained by Empedocles.

The following table shows the four humors along with their related elements, seasons, places where they form in the body, and the temperaments they create.

Influence and legacy

During the Golden Age of Islam, doctors used a medical theory called humorism, which came from ancient Greek and Roman ideas. This theory was explained in detail by the Persian scholar Avicenna in his book The Canon of Medicine (1025). Avicenna described the four humors—blood, phlegm, yellow bile, and black bile—and how they influenced a person's health and personality.

The Unani system of medicine, practiced in Perso-Arabic countries, India, and Pakistan, is based on the ideas of Galen and Avicenna. It focuses on the four humors as a central part of medical practice.

The humoral system believed that each person had a unique balance of the four humors. This idea was used by Greek, Roman, and Islamic doctors starting with Hippocrates. European doctors followed this theory until the 1500s, when Andreas Vesalius began to question Galen’s ideas about the body.

In the 1700s, treatments like bloodletting, using emetics, and applying hot cups to the skin were based on the belief that removing excess humors could help sick people. Medicines called apocroustics were used to stop harmful humors from reaching sick parts of the body.

In the 1500s, the Swiss doctor Paracelsus believed that healing substances could be found in herbs, minerals, and alchemical mixtures. These ideas shaped Western medicine until the 1600s. Specific herbs and minerals were used to treat illnesses, such as chamomile to reduce heat and excess bile, and arsenic in poultices to remove harmful humors linked to the plague. Medicines called apophlegmatisms were chewed to reduce excess phlegm.

By the 1600s, new discoveries in biology and chemistry began to challenge the humoral theory. However, the theory had influenced Western medicine for over 2,000 years. It declined briefly in the 600s and 700s in the Byzantine Empire due to religious changes, but it returned in the 800s. Today, the practice is considered pseudoscience.

The humoral theory was the main medical idea for more than 2,000 years before modern medicine was developed. It was a key part of the teachings of Hippocrates, known as the "Father of Modern Medicine."

The theory of specific causes for diseases, called specific etiology, further reduced the influence of humoralism. Modern medicine now uses the word "humoral" to describe things like hormones and antibodies, but this is unrelated to the old theory. It simply means "related to bodily fluids."

The idea of humorism was not proven wrong until 1858. No studies tested how bodily fluids affected personality traits because these traits were not clearly defined until the late 1900s.

Ancient thinkers like Theophrastus linked personality types to the four humors. People with too much blood were called sanguine, those with too much phlegm were phlegmatic, those with too much yellow bile were choleric, and those with too much black bile were melancholic. These ideas influenced plays by Menander and Plautus. The theory also appeared in European art, such as paintings and prints.

In Shakespeare’s play The Taming of the Shrew, a character named Petruchio uses methods based on the humoral theory to change another character’s behavior. For example, he avoids giving choleric people food they are supposed to avoid, deprives them of sleep, and exposes them to cold weather, which was believed to calm choleric temperaments.

The theory of the four humors is also featured in the 2005 novel Divided Kingdom by Rupert Thomson.