We all know, by watching Sweeney Todd, that barbers got up to some very odd things in the past. From about 1000 AD to well into the 1800s, they were not just hair choppers but well-known surgeons. They'd do everything from pulling teeth to blood letting to castration. But why?
It was in Europe that saw the most organized surgeon-barbers in the world. In the 1500s, Henry VIII even grouped barber-surgeons into guilds and forced them to distinguish themselves from regular surgeons. But barbers became surgeons in different cultures and on different continents. Buddhist monks used barbers as simple surgeons. Egyptian barbers examined and cleaned teeth. Chinese barbers castrated eunuchs - a practice that was emulated in the middle ages when castrati singers were popular.
In the end, barbers became surgeons in early history the same way gun slingers became enforcers in the Old West - they happened to be the people with the right tools and enough experience to use them. The gunslingers had a horse and a gun, and the barbers had a set of knives that they kept sharp and clean, and they had a great deal of practice with them. Since barbers doubled as manicurists, they became adept had digging out hangnails and ingrown nails and hair. They also lanced boils and minor skin irritants. Their knives got them called in to castrate animals, from which castrating humans was relatively similar. They began by checking the mouth for infections and cavities and eventually came to pull teeth and lance infected gums. As their knowledge and skill set was built up, they took on apprentices, who learned similar surgeries by doing.
There were top-level practices that caused qualified physicians to pull out of the trade as well. Some cultures had taboos against interfering physically with the body. The Pope famously banned priests from bloodletting. Meanwhile feudal lords, who imposed justice on their territories, would put doctors to death for malpractice so few were likely to attempt anything as risky as surgery. Few people had the money to pay surgeons, anyway, while barbers were cheap.
It was only in the 1800s that dentists, barbers, and surgeons, were separated as professions. For some time, surgery was thought of as a rather low profession among doctors, since barbers shared it medical men, and so people veered away from it as a subject. As knowledge of anatomy and medical procedure became more precise, more patients began surviving more and more elaborate and dramatic surgeries. As fewer barbers were called upon to perform surgery, that aspect of the profession died out. The last barber-surgeon died in the 1820s.