Postnasal drip syndrome, or postnasal drip syndrome, is a general term for a series of clinical symptoms caused by nasal secretions flowing backward into the throat through the posterior nostril. Its causes mainly include chronic sinusitis, allergic rhinitis, nasal polyps and so on. 1. Chronic sinusitis: it is a chronic inflammatory disease that occurs in the mucous membrane of the sinuses, often combined with asthma and chronic obstructive pulmonary disease, which can lead to nasal congestion, purulent nasal discharge, headache and other uncomfortable symptoms. The purulent nasal mucus secreted by chronic rhinitis tends to drip from the posterior nostrils, thus irritating the pharynx as well as the trachea and bronchial tubes, thus causing the appearance of postnasal drip syndrome. 2. Allergic rhinitis: also known as allergic rhinitis, is one of the chronic reactive inflammation of the nasal mucosa, mainly due to contact with or inhalation of certain allergens, which leads to a series of over-excited allergic reactions, resulting in nasal itching, paroxysmal sneezing, a large amount of watery nasal mucus and nasal congestion. Due to the large amount of nasal secretion, it is easy to drip from the posterior nostril and induce postnasal drip syndrome. 3. Nasal polyps: it is a common chronic disease of nasal and sinus mucosa, which is mainly characterized by extremely edematous nasal mucosa forming single or multiple polyps in the middle nasal tract, which can lead to plasma or mucus nasal mucus, sneezing and nasal itching. Secondary to obstructive sinus inflammation, snot may also drip from the posterior nostrils, leading to postnasal drip syndrome. There are a number of causes of postnasal drip syndrome, and a hospital visit is required to make a definitive diagnosis after a systematic examination.