Bloodletting and Humoral Theory

     Humoral theory is an outdated and archaic medical understanding of the human body. It's often mocked, and I can understand why! Things like bloodletting sound barbaric to the modern day. But there was actually some sort of logic to it, albeit incorrect.

     The theory proposed that human health and behavior was determined by the balance of four bodily fluids, known as humors: Blood, phlegm, yellow bile, and black bile.

     Under this system, health was not a default state you lost by accident. Health was an active equilibrium that had to be maintained against constant pressure from the outside world. Food, weather, emotions, sleep, sex, labor, geography, even social behavior were all understood as forces that could tip the body out of alignment.

     Disease, in this framework, was a consequence, rather than an invader.

    That distinction matters. If illness comes from imbalance rather than invasion, then treatment isn’t about destroying an enemy, it’s about correcting excess. This is why bleeding, purging, vomiting, sweating, and dietary restriction were so central. They weren’t an act of cruelty, they were logical attempts to remove what the body had too much of. If a fever was heat, you cooled it. If a patient was lethargic and pale, you stimulated and warmed them. If someone was manic, agitated, violent, sleepless, it was heat and dryness overwhelming the system.

     Humors were tied to temperament, and temperament was tied to personality. A sanguine person wasn’t just healthy, they were warm, social, impulsive. A melancholic person wasn’t just sad, they were cold, dry, introspective, prone to fixation and despair. These weren’t diagnoses layered on top of identity. They were identity. To be sick was to become more yourself in a distorted direction.

     Humoral theory didn’t separate mind and body. Emotional states could cause physical disease, and physical imbalance could warp thought, perception, and behavior. Excess black bile could make someone withdrawn, obsessive, delusional. Excess yellow bile could make someone irritable, aggressive, reckless.

     This is why mental illness wasn’t treated as unreal or imagined, but it also wasn’t treated gently. If your thoughts were disordered, the solution was to discipline the body. Restrict food, induce vomiting, bleed, cool or heat. The suffering was considered corrective. Pain meant something was happening.

     Bloodletting functioned as one of the most direct and literal method of restoring balance, because blood was considered the dominant humor and the easiest to access.

     Timing mattered. Bleeding might be avoided in winter, increased in spring, or synchronized with astrological charts because the body was believed to rise and fall with the same forces governing the natural world. When it failed, it was usually understood not as a flaw in the method itself, but as a failure of judgment, timing, or moderation. Too little bleeding meant the excess remained, too much meant the patient weakened past recovery.

     Practitioners believed that blood did not circulate endlessly through the body, but rather moved in directional flows connected to specific organs and regions. Because of this, where blood was taken from mattered as much as how much was removed. A headache might warrant bleeding from veins in the arm or temple, while lung complaints might be treated by bleeding near the elbow or chest, and reproductive or abdominal issues by veins in the leg or foot. This followed centuries of anatomical tradition inherited from Galen and later medical authorities.

     The most common method, venesection, involved opening a superficial vein with a lancet. These lancets were small, sharp blades designed to create a clean incision rather than a tearing wound. The goal was controlled flow, not trauma. A tourniquet was applied above the site to swell the vein and make it easier to access. 

     Once opened, blood flowed freely into a bowl. Physicians watched the color, thickness, and speed of the blood as it drained. Dark, thick, or clotted blood was often interpreted as corrupted or excessive, while lighter blood suggested depletion. The blood itself was treated as diagnostic evidence.

     The amount removed varied widely depending on the patient and the illness. Some treatments called for only a small quantity, others for repeated bleedings over days or weeks. Excessive bleeding was recognized as dangerous even within humoral theory, though the margin between “therapeutic” and harmful was poorly understood by modern standards. Weakness, fainting, and pallor were often seen as signs that the body was responding, rather than warnings to stop.

    Scarification was used when a more localized effect was desired. Instead of opening a vein, the practitioner made a series of shallow cuts in the skin. Heated cups were then placed over the area. As the air inside cooled, suction drew blood out through the cuts. This method was thought to pull harmful humors from a specific site rather than from the body as a whole. It was commonly used for joint pain, localized inflammation, or conditions believed to involve stagnation rather than systemic excess.

     Leeching occupied a distinct category. Medicinal leeches were carefully sourced and applied to specific areas of the body. Their saliva contained anticoagulants, which allowed blood to continue flowing even after the leech detached. This made the blood loss slower and more prolonged, and therefore, in humoral logic, more gentle and precise. Leeches were often used on children, the elderly, or patients considered too fragile for venesection. The numbing effect of the bite also made it one of the less painful options.

     After bloodletting, wounds were compressed and bandaged. Ointments might be applied to prevent what physicians feared as putrefaction or corruption at the site. Patients were often prescribed rest, restricted diets, or further evacuative treatments to support the rebalancing process.

     Bloodletting was rarely a standalone act, it functioned as part of a broader regimen aimed at reshaping the body’s internal state.

     From within humoral theory, bloodletting was not violent improvisation. It was a measured intervention based on the belief that illness was excess made visible and that removing that excess could restore harmony. The failure of bloodletting did not discredit the system at the time, because outcomes were interpreted through the same framework: either the body was already too compromised, or the balance had not been adjusted with sufficient precision.

     Seen through a modern lens, the practice ranges from ineffective to actively harmful. But historically, it was coherent, systematic, and deeply integrated into how people understood the relationship between the body, the environment, and the self.