Nasal phlegm, also known as secretion, is considered to be caused by acute and chronic rhinitis, sinusitis, allergic rhinitis and other diseases. 1. Acute and chronic rhinitis: mainly caused by viruses, bacteria and various physical and chemical factors and inflammation of the nasal cavity, can lead to nasal mucosa congestion, swelling, exudation, atrophy or necrosis and other pathological changes. This leads to runny nose, nasal congestion, sneezing, itchy nose and other uncomfortable symptoms. 2. Sinusitis: an inflammatory disease of the sinus mucosa, mainly caused by bacterial, fungal and viral infections, which can lead to nasal congestion, thick nasal discharge, head and face pain and loss of smell and other symptoms. 3. Allergic rhinitis: it is a kind of allergic reaction inflammation of nasal mucosa, mainly caused by inhalation allergens and ingestion allergens, which can lead to nasal itching, nasal discharge, sneezing and other uncomfortable symptoms. In addition, respiratory infections, nasal polyps, nasopharyngeal carcinoma can also lead to the phenomenon of nasal phlegm, it is best to go to the hospital in a timely manner, a clear diagnosis.