Mucus at the opening of the throat may be caused by chronic pharyngitis, reflux pharyngitis, rhinitis-sinusitis, trachea-bronchitis and so on. 1. Chronic pharyngitis: under the action of inflammatory factors, it will lead to an increase in oozing from the throat area, thus causing mucus at the mouth of the throat. 2. Reflux pharyngitis: stomach contents reflux into the throat, irritating the mucous membrane of the throat and causing the symptom of phlegm in the throat. 3. Rhinitis – sinusitis: due to the existence of inflammatory reaction in the sinus or nasal cavity, under the stimulation of inflammation, resulting in increased nasal secretion, due to the nasal secretion backflow into the throat, thus making the mouth of the throat with mucus. 4. Chronic trachea-bronchitis, can show phlegm in the throat. Mucus at the mouth of the throat may also be caused by other reasons. If the symptoms persist or are accompanied by other discomforts, it is recommended that you seek medical attention in the hospital for a clear diagnosis and treatment.