A sniffing phlegm is a manifestation of the backflow of nasal mucus, may be suffering from nasopharyngitis, allergic rhinitis, sinusitis and other diseases caused by, it is recommended to consult a doctor in time for examination. 1. Nasopharyngitis: Nasopharyngitis may cause snot to flow backward, the patient will also have nasal congestion, the symptoms will be more obvious at night when resting, may also trigger a runny nose, dry and sore throat and other undesirable symptoms, and some patients will have a fever. 2. Allergic rhinitis: allergic rhinitis, nasal secretions increase, inhalation of the nose will make the secretions flow into the throat, which will cause coughing, coughing up phlegm, the patient will also be itchy nose, sneezing and other uncomfortable symptoms. 3. Sinusitis: Nasal reflux may also be the discomfort caused by sinusitis, nasal secretions will cause nasal reflux when sniffing, there will be such a situation, the patient will be accompanied by sinus pain, headache, dizziness and other undesirable symptoms, severe may make the sense of smell impaired. This symptom requires prompt medical attention, identify the cause of the disease, and actively cooperate with the treatment under the guidance and advice of the doctor.