Most of the nasal mucous membrane glands are secreted due to the nasal cavity mucous glands, the nasal mucous glands contain a kind of cup-shaped cells which can secrete a lot of mucin, and the mucin can absorb a lot of water when it is released to the outside of the cells, thus forming nasal mucus. Another component is tears, which are mainly produced by the tear glands, and part of them will flow to the tear ducts, and since the nasal cavity and the tear ducts are connected through the nasolacrimal ducts, they become part of the nasal mucus. In addition, nasal mucus may also be mixed with dust or microorganisms from outside. So nasal snot also plays the role of keeping the nasal cavity moist if there is no obvious change. If there is a change in the nature, such as yellow sticky or smelly nasal mucus, there is a possibility that infection has occurred.