what cause bronchitis?
<answer> Smoking, inhaling irritating fumes or dust, viruses such as the flu and bacteria. <context> Chronic bronchitis is caused by smoking, inhaling irritating fumes or dust, viruses such as the flu, and. bacteria. Risk factors for chronic bronchitis include advanced age, a weakened immune system, smoking, chronic obstructive pulmonary disease (COPD), and. repeated exposure to lung irritants.