The Four Humours: The Ancient Theory That Ruled Medicine for 2,000 Years

Imagine going to your doctor with a nasty sore throat and leaving with a prescription to have most of your blood drained out of your body. Sounds horrifying? Welcome to medicine, ancient-style — and not so ancient either, as it turns out.

For roughly two thousand years, from the time of the ancient Greeks right up to the 19th century, Western medicine ran on a single, gloriously confident idea: your body contained four fluids, and if they got out of whack, you got sick. Those four fluids — blood, phlegm, yellow bile, and black bile — were known as the humours. Keep them balanced and you’d live a long, healthy life. Let one tip over, and your doctor would do something deeply unpleasant to restore order.

The theory likely has roots in Ancient Egyptian and Mesopotamian medicine, but it was the ancient Greeks who really ran with it. Hippocrates, the bloke we still call the Father of Medicine, is most often credited with nailing down the four fluids specifically. Before Hippocrates came along, illness was considered the work of angry gods or demonic possession. For the first time in history, people started asking not who caused illness, but by what process it actually occurred. That was, genuinely, a revolutionary shift in human thinking.

The theory was elegantly neat, which is probably why it stuck around for so long. Each of the four humours connected to one of the four seasons — yellow bile with summer, black bile with autumn, phlegm with winter, and blood with spring. They also mapped onto the four elements of earth, water, fire, and air. Everything was tidily interconnected, like an ancient Greek version of a wellness wheel, only with considerably more bile in it.

Where things get genuinely fascinating is the personality side. The variant mixtures of the humours in different people determined their complexions, their physical and mental qualities, and their dispositions. The ideal person had the perfectly proportioned mixture of all four. A person with too much blood was sanguine — cheerful, sociable, enthusiastic, basically the life of the party. Too much yellow bile made you choleric, meaning angry, ambitious, and frankly a nightmare at dinner. An excess of black bile produced a melancholic personality, and the word melancholy itself comes directly from the Greek for black bile. Those with too much phlegm were phlegmatic — and we still use that word today to describe someone who is calm, composed, and reliably unbothered by everything.

So the next time you call someone melancholic, or describe your colleague as utterly phlegmatic in the face of a looming deadline, you are, without realising it, quoting a medical theory from 400 BC. Language is a wonderful time capsule.

Now, about the treatments. This is where things get a bit medieval, even when they weren’t technically medieval at all. The physician’s task was to diagnose which humour was out of balance, then focus on restoring equilibrium — either through diet or by reducing the offending humour by evacuating it. Evacuating, in this context, meant bloodletting, purging, inducing vomiting, or administering enemas. Sometimes all four, presumably on a bad day. Even a change in season, a sudden shift in weather, or the onset of puberty was considered a potential health crisis requiring intervention. Imagine being a medieval teenager with that on top of everything else.

Bloodletting became the superstar treatment of the humoral era. Bloodletting rose dramatically in popularity around 160 CE, when Galen became the dominant medical voice in Rome, with patients who included some of the most powerful figures in the Roman Empire. At its peak, the practice was so pervasive that the word “leech” became common slang for “doctor.” Paris hospitals in the early 19th century reportedly got through five to six million leeches per year. Five to six million. The logistics alone are staggering.

The most poignant — and frankly alarming — example of humoral medicine in action involves America’s first president. George Washington woke at 2am on 14 December 1799 with a sore throat and severe difficulty breathing. His doctors proceeded to drain roughly 80 ounces of blood over 12 hours — around 40 percent of an adult’s total blood volume. Washington died that evening. His doctors were not rogue quacks. They were the best physicians of their time, following the best available medical thinking, completely convinced they were helping. The red and white barber’s pole you still see on the high street today is a direct symbol of this era — red for the blood let, white for the bandages applied afterwards. Your local barber’s shop is carrying a 2,000-year-old reminder that medicine used to be done with scissors and a bucket.

By the late 1700s, Joseph Priestley and Antoine Lavoisier had blown up Aristotle‘s four-element explanation of the physical world. By the late 1800s, germ theory offered an entirely new way of understanding disease. The humours quietly lost their grip on medicine, though bloodletting stubbornly hung on — it was still being recommended in a major medical textbook in 1923.

Yet the theory didn’t disappear entirely. It just changed form. In the 20th century, psychologists like Hans Eysenck began identifying personality dimensions such as extraversion and neuroticism. Researchers found these dimensions clustered in patterns remarkably reminiscent of the ancient humours — high extraversion with high emotional reactivity echoing the choleric type, calm and low-reactive personalities resembling the phlegmatic. Modern personality frameworks including DISC, Myers-Briggs, and even the Big Five all carry echoes of Hippocrates in their bones, whether their creators knew it or not.

Shakespeare wrote the humours into his plays. An excess of the hot, dry choler produced an angry disposition — valuable in great warriors but a social problem in domestic life. In The Taming of the Shrew, Petruchio’s entire strategy for dealing with Katherina is essentially a humoral therapy programme, withholding food and rest to cool her excess yellow bile. The medical establishment would have nodded approvingly.

What the four humours story really tells us, underneath all the leeches and the bile, is something quite humbling about human knowledge. Hippocrates and Galen were not fools. They observed carefully, they built logical systems, and they genuinely tried to understand a universe they lacked the tools to fully see. Their mistake was not stupidity. Their mistake was confidence — the same confidence, incidentally, that every era of medicine has shown in its own theories. For people at the time, most of those treatments made sense and, at least some of the time, appeared to work. Self-limiting illnesses recover on their own. Post-recovery, the bloodletting gets the credit.

So perhaps the most useful thing the four humours can teach us today is a little intellectual humility. We call ourselves sanguine when things go well, melancholic when the world feels grey, choleric when traffic is bad, and phlegmatic when we simply cannot be bothered to care. The Greeks gave us our emotional vocabulary, even as their medicine turned out to be spectacularly, leech-consumingly wrong. And somewhere in that contradiction is a very human story about how we make sense of the world with whatever tools we happen to have at the time.