Chronic Postnasal Drip (Upper Airway Secretion Syndrome): This is often the most common cause of a chronic cough, resulting from the drip of secretions from the nose or sinuses into the throat, triggering cough.

Asthma: A chronic inflammatory disease of the airways that can cause cough, wheeze, shortness of breath, and chest tightness. Cough can be the sole presenting symptom.
Gastroesophageal Reflux Disease (GERD): Stomach acid reflux into the esophagus can trigger a cough, often worse at night or after eating.
Chronic Bronchitis: Part of chronic obstructive pulmonary disease (COPD), characterized by a chronic cough with mucus production, typically in smokers.

Lung Cancer: Although less common, lung cancer can present with a chronic cough, and given its severity, it's crucial not to miss this diagnosis, especially in smokers or those with a significant smoking history.
Tuberculosis (TB): A chronic infection that can cause cough, fever, night sweats, and weight loss. It's essential to consider TB, especially in individuals who have been exposed or have risk factors such as immunocompromised states.
Pulmonary Embolism: While typically presenting acutely, in some cases, a pulmonary embolism can cause a chronic cough, especially if it leads to pulmonary infarction.

Cystic Fibrosis: An inherited disorder that causes severe damage to the lungs, digestive system, and other organs in the body. It can present with a chronic cough in adults who were not diagnosed as children.
Sarcoidosis: A disease characterized by the growth of tiny collections of inflammatory cells (granulomas) in any part of the body — most commonly the lungs and lymph nodes. It can cause a chronic cough among other symptoms.
Eosinophilic Bronchitis: A condition characterized by inflammation of the airways with eosinophils, which can cause a chronic cough without asthma or airflow obstruction.