Chronic Bronchitis: This is often the most common cause of a persistent cough, especially in smokers or those exposed to pollutants. The chronic inflammation of the bronchial tubes leads to a persistent cough, often productive of mucus.

Asthma: A chronic condition characterized by inflammation and constriction of the airways, leading to coughing, wheezing, and shortness of breath. Asthma can cause a persistent cough, especially at night or with exercise.
Gastroesophageal Reflux Disease (GERD): Stomach acid flowing back into the esophagus can irritate the throat and lungs, causing a persistent cough. This is more common in individuals who experience heartburn or regurgitation.
Postnasal Drip (Upper Airway Secretion Syndrome): Mucus from the nose draining down the back of the throat can cause a persistent cough, especially when lying down.
Allergic Rhinitis: Similar to postnasal drip, allergies can lead to increased mucus production, which may irritate the throat and cause coughing.

Lung Cancer: Although less common, lung cancer can present with a persistent cough, especially if it involves the central airways. It's crucial to consider this diagnosis, especially in smokers or those with a significant smoking history.
Tuberculosis (TB): A bacterial infection that primarily affects the lungs and can cause a persistent cough, often accompanied by weight loss, fever, and night sweats. TB is more common in immunocompromised individuals or those from endemic areas.
Pneumonia: While often presenting acutely, some forms of pneumonia (such as walking pneumonia) can cause a persistent cough. It's essential to consider pneumonia, especially if the cough is accompanied by fever, chest pain, or difficulty breathing.
Pulmonary Embolism: Although typically presenting with acute symptoms, in some cases, a pulmonary embolism can cause a persistent cough, especially if it's small and doesn't cause immediate significant symptoms.

Cystic Fibrosis: A genetic disorder that leads to the production of thick, sticky mucus, causing persistent coughing and lung infections. It's rare in adults without a previous diagnosis but should be considered in those with a suggestive family history or other symptoms like pancreatic insufficiency.
Sarcoidosis: An inflammatory disease that can affect multiple parts of the body, including the lungs, leading to a persistent cough among other symptoms.
Bronchiectasis: A condition characterized by damaged, widened airways, leading to a persistent cough and frequent lung infections. It can be congenital or acquired due to various causes, including infections or autoimmune diseases.