Reasons for the build-up of excess mucus in the lungs include a viral or bacterial infection of the airway or, in chronic cases, smoking, according to WebMD. Viral infections typically cause milder symptoms, while bacterial infections tend to cause more serious symptoms. Either can lead to a diagnosis of acute bronchitis or pneumonia. Chronic bronchitis is a condition in which coughing due to excess mucus and inflammation occurs every year, persisting for at least a couple months each time.
Acute bronchitis is typically less severe than pneumonia, states WebMD. In both conditions, the body coughs up the excess mucus; however, with pneumonia, the mucus tends to be a darker color. Pneumonia may also cause fever, shortness of breath, chest pain and other symptoms that present somewhat suddenly. A common treatment for pneumonia is a course of antibiotics, which typically clears up the underlying infection.
Although smoking is the most common cause of chronic bronchitis, it may also be the result of infection or exposure to industrial fumes or dusts, according to the American Lung Association. A person with chronic bronchitis is also at a higher risk of lung infection due to the constant irritation of the airways. Without treatment, chronic bronchitis may progress to a more serious condition, such as emphysema.