In winter, many outpatients have a cough after a cold, which often lasts longer, up to 2 weeks or even several months, and according to recent experience in the clinic, it seems to be better in young people than in older people. The cough is often paroxysmal, mostly affecting sleep, and is treated with a variety of antibiotics with poor results and is very painful. What should we do in this case? There is some debate about the definition of a chronic cough, with most people referring to a cough that has been present for more than 32 weeks as a chronic cough. Chronic cough often has the following causes: 1. Coughing after a cold: Increased airway reactivity after a cold. As colds are mostly viral infections, they tend to sensitize the airways, leading to increased airway reactivity. For asthma patients, it is easy to induce asthma. In my experience, for patients with 1-2 weeks of cough after cold, if chest X-ray and blood picture are normal, some bronchodilators such as theophylline and montelukast can be added appropriately for treatment, and the patients’ cough relief will be accelerated. 2. Variant asthma: easily misdiagnosed as chronic bronchitis. Both have cough as the only or main symptom, no obvious abnormalities on chest X-ray, and both have self-remitting periods. The former often has allergic diseases such as urticaria, skin eczema, and allergic rhinitis. Allergen skin tests are often positive for one or several antigens. The nature of the cough is different. The former is unusually violent, persistent and unresolved, with a predominantly paroxysmal spasmodic dry cough, occasionally with a small amount of mucous sputum, with nocturnal or morning attacks that interfere with sleep and are aggravated by cold air or exercise induction, and ineffective anti-inflammatory and phlegm-suppressing cough medications. Positive bronchial excitation test or diastolic test. 3. Postnasal drip syndrome (PNDS) PNDS was first proposed by American scholars and refers to a syndrome in which rhinitis or sinusitis causes secretions to flow backwards behind the nose and throat, resulting in a cough as the main manifestation. However, this definition has not been widely accepted. Instead of using the diagnostic term PNDS, European scholars use the term “rhinitis/sinusitis” to refer to cough caused by nasal disease. The main reason for this is that some coughs caused by upper airway disease do not have the typical postnasal drip, cobblestone sign, or pharyngeal mucus adhesion sign. In addition, it is not possible to clarify whether upper airway-related cough is caused by direct stimulation of the postnasal drip or by direct stimulation of the upper airway cough receptors by inflammation. For these reasons, in 2006, the American College of Chest Physicians (ACCP) Cough Guidelines Committee revised the 2nd edition of the U.S. Cough Guidelines and recommended replacing PNDS with “upper airway cough syndrome” (UACS). The 2009 edition of the guidelines adopted this new diagnostic terminology and extended and expanded the definition of UACS. In the 2nd edition of the US cough guidelines, the definition of UACS is still limited to the category of rhinitis and sinusitis. In fact, in addition to rhinitis and sinusitis, upper airway diseases such as chronic pharyngitis, chronic tonsillitis, and even tongue lesions can cause cough. Therefore, the 2009 edition of the guidelines defines UACS to include both of these diseases. Although the diagnostic terminology of UACS was introduced, the 2009 edition of the guideline also retained the diagnostic terminology of PNDS, in consideration of the continuity of the guideline on the one hand, and because the diagnostic terminology of PNDS is easier to understand for some patients with typical postnasal drip influenza on the other hand. 4. Gastroesophageal reflux cough: cough is one of the most common extraesophageal symptoms of GERD, followed by pharyngeal bulb sensation and/or foreign body sensation in the throat, burning pain in the throat, and hoarseness. The cough is mostly irritating and dry, but can also be characterized as a cough with sputum. Most of the coughs are daytime coughs, and some of them are nocturnal coughs, often accompanied by heartburn, acid reflux, chest pain, nausea and other digestive symptoms. However, there are also many patients who have no reflux symptoms at all, and cough is their only clinical manifestation. 24H esophageal PH monitoring is diagnostic. The mechanism is unclear and may be related to the stimulation of cough receptors in the pharynx, larynx and trachea by reflux. It can be rapidly alleviated with acid-suppressants or gastrointestinal stimulants (e.g. morpholine) or H2 receptor blockers or proton pump inhibitors, but significant improvement takes up to 5 months. Chinese medicine is more effective in relieving the disease. The 2005 edition of the guidelines included bronchial tuberculosis as a cause of chronic cough for the first time. At that time, “endobronchial tuberculosis” was used because the name was “familiar” to clinicians. However, in reality, the bronchi do not have an anatomical structure called the “lining”. Therefore, the 2009 edition of the guideline discards this unstandardized term and replaces it with “tracheobronchial tuberculosis”. These are the common causes, but others, such as lung cancer, bronchitis, and ACEI medications, should not be left out. The following is the diagnostic process for reference.