Gastroesophageal Reflux Disease (GERD): This is often considered the most likely diagnosis for chronic cough due to its high prevalence and the fact that cough can be the sole presenting symptom of GERD. The mechanism involves acid reflux irritating the upper airway, triggering a cough.

Asthma: Chronic cough can be a manifestation of asthma, especially in cases where wheezing and shortness of breath are not prominent. The cough in asthma is typically dry and can be exacerbated by triggers such as allergens or exercise.
Chronic Obstructive Pulmonary Disease (COPD): COPD, which includes chronic bronchitis and emphysema, often presents with a chronic cough, typically productive of sputum. This diagnosis is more likely in smokers or those with a history of significant smoke exposure.
Allergic Rhinitis: Postnasal drip from allergic rhinitis can cause a chronic cough. This is often accompanied by other symptoms such as sneezing, runny nose, and itchy eyes.
Upper Airway Secretion Syndrome: This includes conditions like postnasal drip from various causes (allergic, non-allergic, or infectious rhinitis), where secretions drip down the back of the throat, triggering a cough.

Lung Cancer: Although less common, lung cancer can present with a chronic cough, especially if the tumor involves the airways. It's crucial to consider this diagnosis, particularly in smokers or those with a significant smoking history.
Tuberculosis (TB): TB can cause a chronic cough, often accompanied by systemic symptoms like fever, night sweats, and weight loss. It's a critical diagnosis not to miss due to its infectious nature and the need for public health intervention.
Pulmonary Embolism: While typically presenting acutely, chronic or recurrent pulmonary emboli can cause a chronic cough. This diagnosis is critical due to its high mortality rate if untreated.
Cardiac Failure: Heart failure, particularly congestive heart failure, can lead to a chronic cough due to pulmonary congestion. This diagnosis is vital to recognize due to its implications for cardiac function and the need for specific management.

Cystic Fibrosis: Although more commonly diagnosed in childhood, cystic fibrosis can present in adulthood with a chronic cough, among other symptoms like recurrent infections and malabsorption.
Bronchiectasis: This condition, characterized by permanent dilation of parts of the airways, can cause a chronic cough, often productive of large volumes of sputum.
Sarcoidosis: A systemic granulomatous disease that can affect the lungs, causing a chronic cough, among other symptoms like shortness of breath and chest discomfort.
Eosinophilic Pneumonia: A rare condition characterized by an accumulation of eosinophils in the lungs, which can present with a chronic cough, fever, and respiratory symptoms.