2. Surgical mask: It can block more than 90% of 5 micron particles and should be replaced every day, but it should be replaced immediately if it is damaged or dirty. It is suitable for use when you have respiratory symptoms such as colds, fevers, coughs, etc., and when you go to unventilated places such as hospitals, cinemas, etc.
3. Activated carbon mask: It can absorb organic gas and toxic dust. It does not have the function of sterilization. It should be replaced immediately when it needs to breathe hard or cannot absorb peculiar smell. It is suitable for painting or spraying pesticides.
4. N95 mask: It can block more than 95% of sub-micron particles and has high respiratory impedance. It is not suitable for ordinary people to wear for a long time, and repeated use should be avoided.