Bloodletting, known today as phlebotomy, as both a therapeutic and preventative medical practice can be traced at least to ancient Greece, though it may have originated in Egypt. There is also evidence of its use in ancient China, though it was eventually replaced by acupuncture.

It became an integral component of European medical practice after it was embraced by the Greco-Roman physician, Galen, who believed that most illness stemmed from an overabundance (or plethora) of one or more humors. According to this theory, blood itself was not only a humor but was also believed to contain the other three humors. Thus, bloodletting was believed to be the most effective way remove excess humors from the body. This could be done using a variety of techniques, including cutting a vein, wet cupping, or applying leeches.

Galen’s ideas were hugely influential in shaping medical practices in both the Islamic and European worlds up until the modern period, which helps explain the continued prevalence of bloodletting. In Europe, bloodletting was often prescribed by doctors, but carried out by barber surgeons.

Bloodletting only fell out of regular use after statistical data called its efficacy into question in the 19th century, followed by the replacement of humoral theory with germ theory. Today, it is only used for the treatment of a few illnesses, such as hemochromatosis, which causes the excess build-up of iron. Interestingly, recent research suggests that for some people, regularly donating blood can lead to long-term health benefits, offering some support to the historical practice of preventative bloodletting.