Based on what is known so far, novel coronavirus can be transmitted by droplets/aerosols, surface deposition, and feces/sewage, and from what we know so far, droplet/aerosol transmission is the main mode of transmission, which is what we call airborne transmission. However, since air is the main mode of transmission of novel coronavirus, why do we need to pay attention to ventilation in the protection guidelines? In fact, the human body is not infected with the virus as we think, as soon as it comes into contact, but needs the virus to reach a certain number and be able to break through the body’s immune system before being infected, which is one of the reasons why people with weaker resistance, such as chronically obese people and diabetics, are more likely to be infected with the virus. In a normal environment, the amount of viruses in the flowing air is generally not enough to break through the body’s defense system, so we will not be infected. When the air lacks flow, the virus in the air will gradually settle down and its concentration will slowly become larger, and the possibility of us being infected becomes greater. If someone in the family brings back a virus from outside, if the room is not ventilated, all these viruses will gather indoors and pose a threat to everyone in the family. So in order to dilute these viruses, we should always ventilate the room, and the ultraviolet light outside can also play a role in killing the virus. But if you are in a more dangerous area, such as next to a hospital, then the virus content in the air may be more, and people with long-term obesity, diabetes and other poor resistance in the home will have the possibility of being infected, so it is time to open the windows with a little caution and try to ventilate when the weather is better and the UV rays in the air are stronger.