/kloc-Europe in the mid-0/9th century, when hospitals did not have the concept of disinfection. Doctors wear gray robes and nurses wear nuns. The purpose is to avoid blood on clothes, and choose gray and black to make clothes look less dirty, because these clothes are never washed. At that time, a large number of patients died of bacterial infection, and people did not know that the death of patients was caused by doctors' clothes.

The man who changed all this was Frenchman Louis Pasteur, who was later called "the father of microorganisms". He had five children, only two of whom lived to be adults. Three others died of typhoid fever. This incident prompted him to start studying infection.

He found that bacteria are the cause and medium of various infectious diseases, and high temperature heating can kill microorganisms that make beer bitter. And created the "pasteurization method", which was quickly applied to food and beverage. Pasteur also realized that many diseases are caused by microorganisms, thus establishing a bacterial theory, emphasizing that doctors should use disinfection.

From then on, doctors began to put on clean white coats, began to sterilize surgical instruments at high temperature, washed their hands before operation, and put bandages on patients' wounds after disinfection. This greatly reduces the probability of surgical infection. The white coat naturally replaced the gray robe and became the official work clothes of doctors. Nowadays, "white coat" has become synonymous with the profession of doctors.