The blue color of the mask is outside and the white color is inside. Mask color can be distinguished inside and outside, in principle, the front and back of the mask color more than the same, the outside is mostly light blue or dark, the inner layer is mostly white or light color. There is also a way to distinguish the metal strip, generally the metal strip is on the top of the mask, the side of the metal strip protruding outward is the outside, the opposite side is the inside. The main mode of transmission of the new coronavirus is respiratory droplet transmission and contact transmission. The virus in the patient’s respiratory tract can affect healthy people through any liquid, including sputum, respiratory droplets, saliva, and the gateway to invade healthy people is the mucous membrane, so wearing the mask correctly is the key to block the transmission.