Causes of bronchitis
Allergies - Although allergies will not necessarily causes chronic bronchitis, they can make the symptoms worse.
Chemicals - Working around chemicals for a sustained period of time is a known factor of causing chronic bronchitis. Factory conditions that cause symptoms can manifest as "industrial bronchitis". Asbestos, coal, cotton, and talc are just a few of the many chemicals that can irritate the bronchial tubes to the point of developing chronic bronchitis.
Cigarette smoking - Cigarette smoking is a well known cause of chronic bronchitis. However, even if you are not a smoker, being exposed to second-hand smoking may irritate your bronchial tubes, thus allowing you to get sick more easily with a virus, and so develop acute bronchitis.
Gastroesophageal reflux disease (GERD) - Chronic bronchitis can develop from stomach acids that travel up through the esophagus and then down into the airways.
Viruses - Both the common cold and the flu virus are the most common reasons for acute bronchitis. You may catch these viruses from the air that people breathe, which is then coughed out. Or, you may come into contact with someone's hands or contract a virus via touch.
Other - Bacterial and fungal causes are possible, but occur less frequently.
Bronchitis is a common condition, with treatments available for both conditions (however, chronic bronchitis is significantly more long-lasting and may always have symptoms present). How do you know if you're having symptoms of bronchitis, whether acute or chronic? Read here for more information on the symptoms of bronchitis.