Cough is a very common reflex protective action, an explosive expiratory action caused by physical or chemical irritation of the mucous membrane of the pharynx, larynx, trachea and bronchi by inflammation, foreign bodies, etc., through a nervous reflex. From its definition we can already have a sense of the complexity of its etiology – because it seems that irritation of any part of the respiratory tract can cause cough. To determine the cause of a cough, it is necessary to first classify it from the clinical history: i. According to the length of the history: cough lasting less than 2 weeks → acute cough, cough lasting 2 to 4 weeks → prolonged cough, cough lasting more than 4 weeks → chronic cough. 1. Infectious cough: Cough caused by pathogenic microorganisms such as bacteria, viruses, mycoplasma, chlamydia, fungi, and Mycobacterium tuberculosis that cause infection of the pharynx, larynx, trachea, bronchi, and lungs becomes an infectious cough. As the name implies: pharyngitis, laryngitis, tracheitis, bronchitis, pneumonia, tuberculosis …… 2. Non-infectious cough: i.e., a cough that is not caused by infection of the pharynx, larynx, trachea, bronchus, or lungs by pathogenic microorganisms, but by other causes that irritate the aforementioned areas. Examples include tracheobronchial foreign bodies, tracheobronchial developmental malformations, post-pneumonic phase, bronchiectasis, pulmonary fibrosis, interstitial lung disease, asthma, cough variant asthma, upper airway cough syndrome (cough caused by chronic rhinitis, pharyngitis, etc.), gastroesophageal reflux, etc. What is the connection between these two classification methods? How should the diagnostic idea of cough be established? When we come across a child with a cough as the main complaint in an outpatient clinic, the doctor basically asks, “How long has the child been coughing? “This is the first way of classifying cough according to the length of the medical history, because acute and prolonged coughs are mostly caused by infections, while chronic coughs without repeated infections should be considered as a possibility of other non-infectious diseases. Therefore, when I go to the clinic, if a child has had a cough for more than 4 weeks, the question I immediately ask is “Have you ever had a cough of this duration before?” and then “What caused each cough?” . However, there is no such thing as 100% in medicine, and even if a child has had a cough for more than 4 weeks, it is not always necessary to consider asthma or allergies immediately, because some children will say “I have never had such a long cough before” and then ask further questions to find out that they did have cold symptoms a month ago, and some of them may have a fever, which improved with medication. Some of them may have a fever, but the cough persists. The cough may have improved after medication, but the cough still persists. Or the cough may be better after some medication, and then worsen after getting a cold or contact with a cold patient, or the fever may return. In this case, it is more likely to be an infectious cough. Also ask, “Is there anything stuck in the trachea?” This is because foreign bodies in the bronchial tubes can also cause acute or chronic coughing. Once these questions are known, the next step is to ask about the cause of the cough, the severity of the cough, the accompanying symptoms, whether the cough is heavy during the day or at night, and to determine the extent of the infection based on the results of the lung auscultation, the laboratory tests and the chest X-ray. Tracheitis? Bronchitis? Pneumonia? Or is it a cough caused by airway hyperreactivity during the recovery phase of the infection? It will then be decided whether further tests are needed and how to treat the infection. For coughs with no symptoms of infection and no basis for infection at all, especially prolonged coughs, it is important to look for other causes. Ask about the nature and extent of the cough, be aware of the possibility of bronchial foreign bodies, ask about the presence of symptoms of chronic rhinitis (recurrent nasal congestion, runny nose, sneezing, sleep snoring) and gastroesophageal reflux (recurrent acid reflux, heartburn, nausea, chest pain, pronounced at night) and Their temporal correlation with cough, is there any cough after exercise? Is exposure to a certain food, household object, or environment found to cause coughing and no coughing without exposure? Is there wheezing when coughing? Also look for increased eosinophils in the laboratory tests (suggesting the possibility of allergies), look at the results of chest films or CT (if not, chest imaging should be done), and if necessary, check for allergens and other laboratory tests. This is used to make a preliminary determination of the etiology of the disease, and empirical treatment is given for a review after 1 week to see the effect of treatment and the results of the laboratory tests to analyze whether the previous diagnosis and treatment are correct and to provide guidance for further treatment. Objectively speaking, chronic cough is a symptom that is not easy to diagnose, and its causes are multiple and complex. This requires parents to provide as complete as possible their child’s previous medical history, clinical manifestations, medical records, types of medications and treatment results, as well as previous laboratory test results and films, so that we can work together to find the cause of their child’s recurrent cough. Given that there are a variety of diseases that cause cough and often overlap between them, and that determining the cause is a process that requires flexible and individualized analysis, the diagnosis and treatment of each disease will not be discussed here to avoid confusion. We hope that this section will give you a general idea of your child’s cough and a brief initial impression of the diagnostic ideas for recurrent cough, so that we can communicate better in the clinic. Good luck with your visit and may all your children be healthy!