In the days before modern medical procedures, leeching blood was seen as a cure for many different ailments. Bloodletting, sometimes with leeches, was a practice that consisted of removing blood from the body, thereby restoring a person's health. From ancient times up through the late 1800s, people believed that diseases, especially those with symptoms like fevers and the sweats, were caused by having too much blood in the body. Leeches as medical treatment were used to remove the "harmful" blood in a graphic medical procedure. This led to many premature deaths, even of historic figures like George Washington and King Charles II. Even scarier, in medieval times, sometimes barbers performed the procedure.
Because we understand its applications better today, bleeding someone still has its uses, especially since leech therapy restores blood flow and helps those who have had fingers and even limbs reattached to their bodies.
It's impossible to say when bloodletting first began, but historians are pretty sure that the ancient Egyptians started the practice. The oldest descriptions and depictions of it have been found in Ancient Egypt and Mesopotamia, and these date back to a time over 3,000 years ago. Some of the earliest methods of drawing blood even involved using sharpened wood to tear open the skin. However, these are only the first written and drawn mentions of bloodletting — it may have been practiced even earlier.
During the medieval era, barbers helped doctors out by performing bloodletting procedures on their own; after all, they had sharp implements. The traditional barber pole comes from this practice — their white and red stripes stand for the bandages (white) and the blood (red) of the procedure. Supposedly, these poles resemble the bloody white towels that barbers would display outside their storefronts. Although barber poles in the U.S. occasionally have blue on them, as well, the additional color is viewed by some as the color of the veins that the barbers would open. Barbers were forbidden to practice surgery in the mid-1500s in England, although they still practiced amateur dentistry. And it wasn't until 1745 that barbers and surgeons ceased to share the same trade guild.
The idea of bloodletting centers around Hippocrates's theory of the four humors. He postulated this concept in Greece in 2300 BCE, and it stuck around up through the 19th century. Hippocrates believed that the human body was made up of four humors — black bile, phlegm, yellow bile, and blood. When someone was sick, one or more of their humors was out of alignment, and the only way to fix the issue was by removing some of the humor. So, for example, if the illness had to do with the blood, then bloodletting was in order.
The four humors were also aligned to the seasons, a particular organ, and the elements: black bile equaled winter, earth, and the spleen; the presence of phlegm aligned with autumn, water, and the brain; yellow bile was summer, fire, and the gall bladder; and blood was springtime, air, and the heart. The weather conditions during those seasons helped diagnose the problem and the solution. If someone had a fever and was sweating a lot, then they had too much blood in their bodies.
Bloodletting was usually done in the veins of the elbows or knees, places where the practitioner could easily reach them. However, there are spots on the body that people believed "needed" to be bled that were too small for bloodletting implements. This is where leeches came in. One early practitioner of leeching therapies, Themison, who lived in Greece from 80-40 BCE, stated that leeches could be placed on the fingers, nose, lips, gums, and – even more horrifyingly – a woman's pregnant stomach. These areas of the body are where he believed hemorrhoid veins were located.