Heavy pollution came, half of the country’s cities suffered the most serious air pollution so far this year. Masks, originally only to meet the protection needs of certain special occupations, but in today’s serious air pollution, the choice of protective level of masks has also become the most convenient and effective way of protection for ordinary people. As a practitioner who wears a mask every day, I have a good feeling about masks. Most people look a little cuter or more handsome with a mask on. The mask covers most of your expression, and that’s when you realize that everyone actually has pretty eyes. Medical students who are new to surgery have the illusion that the operating room is full of beautiful women, probably because of this. In 1861, Pasteur discovered the presence of germs in the air that could cause surgical wounds to become infected. So in the late nineteenth century, doctors and nurses began to cover their mouths and noses with gauze. It was in 1918, when the Spanish Flu was raging, that the mask came out of the hospital and became a common item for the public. At first, people used masks made of multiple layers of skimmed gauze. Gauze masks were thick and sweat-absorbent, reusable, easy to wash and inexpensive. Experiments have proven that gauze masks with enough layers can filter out a significant portion of dust and bacteria, and have been the most used type of mask for a long time. As the danger of respirable particles and fine particles in urban air has become more and more important to the public, the filtration rate of gauze masks for particles is still less than 30%. In the context of improving environmental conditions that are difficult to accomplish overnight, finding a reliable mask to filter bad air has become the most practical and easy way of personal protection. Surgeons’ surgical disposable masks are industry-standard medical devices that are divided into three layers: an outer layer with an anti-droplet design, a middle layer of filtration, and an inner layer of moisture-absorbing, non-woven material. These masks are mainly used to protect doctors from droplets and splashes, and the filtration rate of particulate matter is only greater than 30%, while the filtration rate of bacteria can reach more than 95%. The edges of these masks are not designed to fit the shape of the face and can only serve as a shield. These masks are obviously not suitable for use against airborne particles. N95, popular in “extraordinary times” In 2003, during the SARS period, an N95 medical mask shaped like a gas mask became a favorite in the market. Compared with the first two masks, this protective mask is much more professional in terms of dust control. The mask model called N95 is based on the American standard. The standard classifies medical protective masks into three categories and nine models, N for non-oil particles and R and P for oil particles. Non-oily particles include: coal dust, cement dust, acid mist, welding fume, microorganisms, etc.; oily particles include: oil mist, oil smoke, coke oven smoke, etc. Each model is divided into three filtration efficiency levels, respectively 95%, 99% and 100%. n95 means “dust mask with 95% efficiency of filtering non-oil particles”. China’s dust mask standards are not divided so fine, N95 is the minimum standard for such dust masks. At present, it is believed that the most threatening particles to human health in the atmosphere are respirable particles with a diameter of 10 microns or less (PM10), especially those with a diameter of 2.5 microns or less (PM2.5). For these tiny particles, the filtering effect of N95 is worthy of recognition. In the production standard of N95, the test sample as particulate matter is sodium chloride aerosol with a diameter of 0.1~0.5 microns, and the filtration rate of qualified N95 masks for such aerosol should be above 95%. So, if you wear N95 or higher level dust mask correctly, even if the air quality index (AQI) reports heavy pollution, we can feel a little bit more at ease when we go out. When wearing a medical protective mask, you should make sure that it fits your face and keep it closed inside the mask in order to play a good filtering function. After wearing the mask, you should perform an exhalation and inhalation test to make sure there is no air leakage. The protective mask can be reused, but if any part of the mask is broken, fractured or lost, or if you feel an increase in resistance when breathing, it should be replaced. Dust masks are not washable and should be discarded after elimination.