Surgeons wear masks to protect patients from their mouth-borne germs, not the other way around, but Asians wear surgical masks in public for a number of reasons, and they’ve been doing it for a century:
The custom of facemask-wearing began in Japan during the early years of the 20th century, when a massive pandemic of influenza killed between 20 and 40 million people around the world — more than died in World War I. There were outbreaks of the disease on every inhabited continent, including Asia (where it devastated India, leading to the deaths of a full 0.5% of the population). Covering the face with scarves, veils and masks became a prevalent (if ineffective) means of warding off the disease in many parts of the world, until the epidemic finally faded at the end of 1919.
In Japan, a few years later, the Great Kanto Earthquake of 1923, triggered a massive inferno that consumed nearly 600,000 homes in the most populous part of the nation. After the quake, the sky was filled with smoke and ash for weeks, and air quality suffered for months afterward. Facemasks came out of storage and became a typical accessory on the streets of Tokyo and Yokohama. A second global flu epidemic in 1934 cemented Japan’s love affair with the facemask, which began to be worn with regularity during the winter months — primarily, given Japan’s obsession with social courtesy, by cough-and-cold victims seeking to avoid transmitting their germs to others, rather than healthy people looking to prevent the onset of illness.
Then, in the 1950s, Japan’s rapid post-World War II industrialization led to rampant air pollution and booming growth of the pollen-rich Japanese cedar, which flourished due to rising ambient levels of carbon dioxide. Mask-wearing went from seasonal affectation to year-round habit. Today, Japanese consumers buy $230 million in surgical masks a year, and neighboring countries facing chronic pollution issues — most notably China and Korea — have also adopted the practice.
Traditional Chinese Medicine puts a premium on proper breathing and clean air, which may explain some of the masks’ popularity..