Due to the Hippocratic Oath preventing physicians from practicing surgery (a task considered beneath them), barbers would assist monks in bloodletting the sick and diseased (later amputating limbs and treating cysts) due to their use of instruments, such as scissors and razors, used as part of their trade. Soon bloodletting became the duty of the barber-surgeon, after a decree was issued preventing the clergy from shedding blood as this was seen as a blemish on their social status.
The iconic barber's pole originated due to the bloodletting procedure, a supposed cure for many illnesses and diseases which were thought to drain out along with the blood. The red symbolizes blood loss and the white represents the bandages. Some barber poles in America have a blue stripe which supposedly provides a patriotic element with the red and white, but it has also been argued that the blue indicates venous blood with the red for arterial blood. During the bloodletting patients would grip the pole to increase blood flow. Often superstitious, barber-surgeons would also treat patients, epileptic for example, by trepanning the skull so as to release demons.
At one time associated with separate guilds, the barbers and surgeons were combined under the United Company Of Barber Surgeons by Henry VIII in 1540.