Acute Bronchitis: This is often the most common cause of green phlegm, resulting from a viral or bacterial infection that leads to inflammation of the bronchial tubes, producing excess mucus that can appear green due to the presence of an enzyme called myeloperoxidase from white blood cells.

Chronic Bronchitis: A form of chronic obstructive pulmonary disease (COPD), characterized by long-term inflammation and irritation of the bronchial tubes, leading to persistent cough and mucus production, which can be green.
Pneumonia: An infection in one or both lungs that can cause coughing up of green or yellow phlegm, depending on the type of bacteria causing the infection.
Sinusitis: Inflammation or infection of the sinuses can lead to the production of green or yellow mucus, which can be coughed up if it drains down the back of the throat.

Lung Abscess: A rare but serious condition where a pocket of pus forms in the lung, which can cause coughing up of foul-smelling, green or yellow phlegm. Missing this diagnosis can lead to severe complications.
Tuberculosis (TB): A bacterial infection that can cause coughing up of green or yellow phlegm, among other symptoms. TB is less common in some areas but can be deadly if not treated.
Cystic Fibrosis: A genetic disorder that leads to the production of thick, sticky mucus that can be green or yellow, affecting the lungs and digestive system. While rare, it's crucial for early diagnosis and management.

Bronchiectasis: A condition where the airways of the lungs become abnormally widened, leading to a buildup of excess mucus, which can appear green.
Aspiration Pneumonia: Occurs when food, liquids, vomit, or saliva is inhaled into the lungs, potentially causing an infection that could lead to the production of green phlegm.
Allergic Bronchopulmonary Aspergillosis (ABPA): A rare condition in people with asthma or cystic fibrosis, caused by an allergic reaction to a fungus called Aspergillus, leading to the production of green or brown phlegm.