Masks are an important line of defense against respiratory infections and can reduce the risk of new coronavirus infections. Not only do masks prevent droplets from being ejected by the patient, reducing the volume and speed of the spray, they also block virus-containing droplet nuclei from being inhaled by the wearer. According to the current knowledge of the disease, it is important to wear the mask correctly. The general principle of wearing a mask is that it is not necessary to wear a mask in open and ventilated places in non-epidemic areas, and it is necessary to wear a mask when entering crowded or confined public places. In open and ventilated areas with a high incidence of the epidemic, it is recommended to wear a single-use medical mask, and to wear a medical surgical mask or a particulate protection mask when entering a crowded or confined public place. Patients with underlying respiratory diseases need to use protective masks under medical supervision. Cotton gauze masks, sponge masks and activated carbon masks are not protective against viral infections. Content source: Dr. You Lai