Nasal snot and sputum have different sources and different compositions. 1. Different sources: nasal snot is mainly secreted by the mucous membrane of the nasal cavity; sputum is mainly secreted by the mucous membrane of the respiratory tract, such as trachea, bronchial tubes, lungs and other products. 2. Different composition: snot is mainly mucin and water secreted by columnar cells, sometimes the liquid secreted by lacrimal glands will be mixed with it; sputum is mainly a mixture of protein, inflammatory cells, particles, viruses, bacteria and so on. If you do the act of sniffing when you have a cold, it can make the snot go into the phlegm and can be coughed up with the phlegm. With symptoms of runny nose or cough, it is recommended to visit a respiratory medicine department to seek professional medical help to identify the cause and timely treatment to avoid delay.