Postnasal phlegm flowing toward the throat may be caused by suffering from rhinitis, nasopharyngitis, postnasal drip syndrome and other diseases. 1. Rhinitis: If the respiratory tract is infected with pathogens such as coronavirus and coxsackievirus, rhinitis may be induced, leading to an increase in nasal mucosal secretions. When nasal secretions flow into the throat, the patient may feel phlegm flowing from the posterior nasal cavity to the throat. This may be accompanied by symptoms such as nasal congestion and runny nose. 2. Nasopharyngitis: If the patient is exposed to high temperature, dust and smoke for a long time, nasopharyngitis may be induced, resulting in dryness and discomfort in the nose and throat, and mucous secretion that is not easy to cough up. Nasal secretions may flow to the throat after the increase in nasal secretions, making the patient feel that there is phlegm flowing from the posterior nasal cavity to the throat. 3. Postnasal drip syndrome: If you suffer from sinusitis, nasal polyps and other diseases, it may lead to nasal inflammatory secretion backflow, so that the patient feels that there is phlegm in the posterior nasal cavity to the pharynx; the patient may be accompanied by pharyngeal itchiness, coughing, and foreign body sensation in the throat and other symptoms. It is recommended that patients go to the hospital in time to find out the cause of the disease and receive treatment as soon as possible.