The glands in our nose, throat, respiratory tract and gastrointestinal tract constantly produce mucus every day. The mucus produced by the nose is commonly known as nasal mucus, which serves to moisten and envelop and destroy foreign substances such as invading viruses and bacteria so that they cannot cause infection. Usually, the snot mixes with saliva, flows to the back of the throat, and is swallowed unnoticed. When the snot is too much or too thick, it is able to be noticed. Excessive nasal discharge may come out of the nostrils or may flow backwards to the throat. Don’t miss the diagnosis of chronic cough, beware of postnasal drip syndrome: Postnasal drip syndrome (PNDS) refers to the backflow of nasal inflammatory secretions from patients with rhinitis and sinusitis into the nasopharynx, oropharynx and hypopharynx through the posterior nostril, causing irritation to the mucous membrane of the pharynx and causing discomfort in the pharynx, which is one of the important causes of chronic cough. Clinical manifestations: paroxysmal or persistent cough. Most patients have discomfort in the pharynx, foreign body sensation in the pharynx, itching, and phlegm adherence in the posterior pharyngeal wall. Patients with allergic rhinitis have symptoms such as nasal itching, nasal congestion, runny nose, and sneezing. For postnasal drip syndrome (PNDS), there are no uniform diagnostic criteria. It is generally judged based on the patient’s chief complaint and examination. The main symptoms as well as relevant examinations: nasopharyngoscopy, sinus X-ray or sinus C, blood routine, blood biochemistry, etc. confirm the diagnosis. Treatment Treatment is mainly symptomatic, commonly used: nasal cleansers, nasal hormones, anti-allergy drugs, antibiotics, etc. Prevention is important Improve the environment, keep warm, take rest, follow medical advice, and strengthen resistance