A cough that persists for more than 8 weeks without obvious evidence of lung disease is now considered to be a chronic cough, and cough is often the only symptom for which patients are seen. Cough is one of the common clinical symptoms of the respiratory system. Chronic cough involves multiple etiologies, not only related to the respiratory system, but also to the nasopharynx and the digestive system. The four major causes of chronic cough are: upper airway cough syndrome, cough-altering asthma, eosinophilic bronchitis, and gastroesophageal reflux. I. Cough allergic asthma 1. Definition: It is a special type of asthma in which cough is the only or main clinical manifestation without obvious symptoms or signs such as wheezing and shortness of breath, but with airway hyperresponsiveness. 2.Clinical manifestations: It mainly manifests as an irritating dry cough, which is usually more intense, with nighttime cough as its important feature. Cold, cold air, dust and oil fumes can easily induce or aggravate the cough. 3. Diagnosis: Conventional anti-infection treatment is ineffective, and bronchodilator treatment can effectively relieve cough symptoms, and this point can be used as the basis for diagnosis and differential diagnosis. Lung ventilation function and airway hyperresponsiveness examination are key methods to diagnose cough allergic asthma. II. Upper airway cough syndrome 1. Definition: It is a syndrome in which secretions flow backward behind the nose and throat due to nasal diseases, or even backward into the voice box or trachea, resulting in cough as the main manifestation. 2. Clinical manifestations: In addition to cough and sputum, patients usually complain of flu drip in the throat, mucus adhesion in the oropharynx, frequent throat clearing, throat itching discomfort or nasal itching, nasal congestion, runny nose, sneezing, etc. Sometimes patients complain of hoarseness and speech induced cough, but other causes of cough itself also have such complaints. Often the onset is preceded by a history of upper respiratory tract disease (e.g., cold). 3. Diagnosis: The underlying diseases causing postnasal drip syndrome include seasonal allergic rhinitis, perennial allergic rhinitis, perennial non-allergic rhinitis, vasodilatory rhinitis, infectious rhinitis, fungal rhinitis, common cold, and paranasal sinusitis. Those with large amounts of sputum are mostly due to chronic sinusitis. Vasodilatory rhinitis is characterized by large amounts of thin, watery nasal discharge sometimes produced in response to changes in temperature. Imaging signs of chronic sinusitis are mucosal thickening of the paranasal sinuses of more than 6 mm, air-fluid planes, or sinus cavity obscuration. Allergen skin prick testing is helpful if the cough is seasonal or if the history suggests an association with exposure to specific allergens (e.g., pollen, dust mites). When allergic fungal sinusitis is suspected, skin tests for Aspergillus and other fungi and specific IgE testing are feasible. C. Eosinophilic bronchitis 1. Definition: A non-asthmatic bronchitis characterized by airway eosinophil infiltration, which is an important cause of chronic cough. 2. Clinical manifestations: The main symptom is chronic irritant cough, which is often the only clinical symptom. It is usually a dry cough with occasional little mucous sputum, which can be coughed during the day or at night. Some patients are sensitive to fumes, dust, odors or cold air, which are often triggering factors for coughing. Patients do not have symptoms such as shortness of breath or dyspnea. Pulmonary ventilation function and peak expiratory flow rate variability are normal, and there is no evidence of airway hyperresponsiveness. 3. Diagnosis: The clinical manifestations lack characteristics, and some of them resemble cough allergic asthma. There are no abnormal findings on physical examination, and the diagnosis mainly relies on induced sputum cytology examination. 4. Gastroesophageal reflux cough 1. Definition: Reflux of gastric acid and other gastric contents into the esophagus, resulting in a cough as the prominent clinical manifestation. 2. Clinical manifestations: Typical reflux symptoms are burning sensation behind the sternum, acid reflux, belching, chest tightness, etc. Patients with gastroesophageal reflux who have trace aspiration are more likely to have cough symptoms and throat symptoms in the early stage. There are also many patients who have no clinical symptoms of reflux and whose cough is the only clinical manifestation. The cough mostly occurs in the daytime and in the upright position, with a dry cough or a small amount of white mucous sputum. 3. Diagnosis: The patient’s cough with reflux-related symptoms or cough after eating is of some significance in suggesting the diagnosis. 24-hour esophageal pH monitoring is currently the most effective method for diagnosing gastroesophageal reflux cough by dynamically monitoring changes in distal and proximal esophageal pH, with results expressed as Demeester’s score, SAP. Barium meal examination and gastroscopy have limited diagnostic value for GERC and cannot determine the correlation between reflux and cough.