Currently we usually classify coughs as acute (less than 3 weeks), subacute (3 weeks-8 weeks) and chronic (more than 8 weeks). Acute coughs can be classified into 2 types depending on whether they are life-threatening or not. Life-threatening acute coughs, such as those caused by pneumonia, asthma or exacerbation of chronic obstructive pulmonary disease, pulmonary embolism, cardiac failure, and other serious diseases; and non-life-threatening acute coughs, such as infections (upper and lower respiratory tract infections), exacerbations of pre-existing diseases, and environmental and occupation-related acute coughs. Subacute coughs are divided into post-infectious and non-infectious coughs. Post-infectious cough includes cough caused by pneumonia or other serious diseases, whooping cough, bronchitis, and exacerbations of new or pre-existing diseases (upper airway cough syndrome, asthma, gastroesophageal reflux, and bronchitis). Common causes of chronic cough include upper airway cough syndrome, asthma, eosinophilic bronchitis and gastroesophageal reflux, in addition to smoking or taking angiotensin-converting enzyme inhibitors. Because chronic cough patients have few concomitant symptoms, no obvious abnormalities on X-ray, and few diagnostic clues, and because physicians do not pay enough attention to them, they are often misdiagnosed and missed clinically. In addition, these patients usually have their own specific etiological distribution. Many patients have been misdiagnosed as “bronchitis” or “chronic bronchitis”, and many of them have been suffering from the disease for several years, which seriously interferes with the patients’ daily life, study and work. Due to unclear diagnosis, these patients are either repeatedly treated with various antibiotics or repeatedly undergo various meaningless tests, resulting in a great waste of medical resources. The most common cause of cough is post-cold cough. Due to the invasion of the virus into the upper respiratory tract, the secretion of the mucous membrane of the trachea and nasal cavity increases, and the patient develops a runny nose, nasal congestion, and phlegm. The throat, stimulated by the presence of phlegm, makes reflex actions such as contraction and coughing in order to remove the phlegm. This upper respiratory tract infection or infection of the lower respiratory tract can usually be cured after a few days of treatment. Coughing is actually a protective reflex of the body. When the upper and lower respiratory tracts are stimulated by excessive secretions, harmful gases, or foreign objects that mistakenly enter the airway, a persistent or strong cough is produced in an attempt to remove the foreign objects. However, frequent and prolonged coughing can affect the patient’s life, sleep, and even his or her respiratory and cardiac functions, making coughing of this nature a pathological condition. To cure a cough, one should first go in search of the cause of the cough. For post-infectious cough in adults (if not bacterial sinusitis or early B. pertussis infection) the following is recommended: antibiotic therapy is not valuable; try inhaled ipratropium bromide; if the cough persists after ipratropium inhalation and affects the patient’s quality of life, consider inhaled adrenocorticotropic hormone; for coughing episodes after severe infection, consider short-term oral adrenocorticotropic hormone after excluding other causative factors Consider short-term oral adrenocorticotropic hormones after other causes; central cough suppressants, such as codeine and dextromethorphan, should be used only when other methods are ineffective. Most distressing for patients is chronic cough, which is often the only reason for their visit. There are many common diseases that cause chronic cough, such as chronic throat diseases: chronic pharyngitis, chronic laryngitis, pharyngeal tuberculosis, laryngeal cancer; chronic bronchial diseases: chronic bronchitis, chronic wheezing bronchitis, bronchiectasis, bronchial carcinoma, alveolar carcinoma; chronic lung diseases: pulmonary tuberculosis, pulmonary abscess, pulmonary cyst, pulmonary schistosomiasis, pulmonary encapsulation, silicosis, pneumoconiosis, alveolar protein deposition, diffuse interstitial lung Fibrosis. There are several other diseases that are less familiar, namely: postnasal drip syndrome (the new term upper airway cough syndrome has now been adopted in the United States to replace postnasal drip syndrome), bronchial asthma, eosinophilic bronchitis, gastroesophageal reflux disease, and due to chronic cardiac insufficiency and medications. The first three of these diseases account for 90% of the causes of chronic cough, and we introduce them separately below. 1. Upper airway cough syndrome: It is not well understood whether the cough associated with the upper airway is related to mechanisms such as postnasal drip, direct irritation or inflammation of the upper airway. The diagnosis of upper airway cough syndrome, which is a syndrome rather than a specific disease, should be determined based on symptoms, signs, imaging and response to treatment. When inflammatory secretions from the nose and sinuses flow back into the pharynx or airways, coughing can occur due to irritation. We commonly see patients with rhinitis and sinusitis in the clinic who present to the respiratory department with poor success with symptomatic medications and are diagnosed only after a follow-up history and detailed examination. First-generation antihistamines or mucosal decongestants are preferred for the empirical treatment of upper airway cough syndrome. 2. Bronchial asthma: It is generally characterized by episodes of wheezing and dyspnea. However, there is a special type of asthma, medically known as “cough variant asthma” or “cough asthma”, which is characterized by a persistent cough, mostly at night or in the early hours of the morning, sensitive to irritating odors, often with an irritating cough, and no croup on lung examination. Croup is often absent on lung examination. These patients are often misdiagnosed as having chronic bronchitis or chronic laryngitis, and their quality of life is seriously affected by the long-term use of antibiotics without relief. These coughs have the following four characteristics: (1) a cough that is predominantly nocturnal or early in the morning; (2) a prolonged dry cough with little sputum; (3) a cough that is aggravated by cold air or irritating odors; and (4) unsatisfactory results of prolonged antibiotic treatment. The diagnosis can be confirmed by a bronchial provocation test or a dilatation test. Treatment with inhaled hormones and bronchodilators can completely relieve cough symptoms. 3. Eosinophilic bronchitis: It is also one of the most common causes of chronic cough. Induced sputum cytology, pulmonary ventilation and airway hyperresponsiveness tests are the key methods for diagnosing eosinophilic bronchitis and cough variant asthma, and pulmonary ventilation and airway hyperresponsiveness tests are now largely popular. The induction sputum test itself does not require complicated techniques and instruments, and therefore has been included as a first-line test for chronic cough. 4. Gastroesophageal reflux disease: Gastroesophageal reflux can cause chronic cough is something that many people do not easily think about. According to the literature, chronic cough caused by GERD accounts for about 20% of cases. This is due to irritation of the lower esophagus by the reflux entering the esophagus, causing an abnormal nerve response and resulting in respiratory spasms that produce a cough. If the patient often has symptoms such as acid reflux, heartburn, and foreign body sensation in the throat, and if the cough symptoms are associated with satiety, recumbency, sleep, and alcohol consumption, the cough should be considered as possibly related to a digestive disorder. Once the diagnosis is established, the doctor will treat the cough with appropriate medication or anti-reflux surgery, which can result in significant relief. 5. Chronic bronchitis: Chronic bronchitis is a common and frequent disease in China. Chronic bronchitis cough is characterized by a cough with a large amount of sputum coughed up, predominantly in the morning, and increased and purulent sputum with acute infection, turning yellow in color. Chronic bronchitis often has a history of more than 2 years, and the cough lasts for more than 3 months each year. Its treatment, first of all, is to quit smoking, strengthen exercise, enhance physical fitness and reduce the number of episodes of respiratory infection. 6. Drug effects: Many drugs can cause coughing, such as commonly used drugs for hypertension, i.e. angiotensin-converting enzyme inhibitors, such as Kaipotong, Yuetinin, Lodinin, etc.; amiodarone and diuretics can also cause coughing. According to the literature, cough is a common side effect of taking angiotensin-converting enzyme inhibitor antihypertensive drugs, with an incidence of about 10%-30%, accounting for 1%-3% of the causes of chronic cough. Once cough symptoms occur with these drugs, the cough can be relieved if the drug is discontinued immediately. Therefore, patients should be reminded to read the instructions carefully before using the medication so that they are well informed. In addition, when cough is mentioned, many people naturally think of respiratory diseases and tend to ignore diseases of other systems. Cough receptors are not only found in the respiratory system such as the pharynx, trachea and bronchi, but also in the esophagus, paranasal sinuses, external auditory canal, pleura and pericardium, etc. Any lesion in these systems or areas may produce cough symptoms. Therefore, in addition to the respiratory system, attention should also be paid to lesions of the digestive, otorhinolaryngological, and cardiovascular systems. Cough is also associated with a history of specific occupational exposures, such as warehouse dust, dust mites, pollen, silk, and mushroom spores, etc. Occupational exposure to chemicals or chemical products, such as latex gloves and acrylic salts, has also been reported. Cardiac insufficiency can also manifest as cough, especially in those with wheezing after activity and nocturnal paroxysmal dyspnea.