The causes of chronic bronchitis are not yet very clear. It is currently speculated that it may be the result of multiple factors interacting over a long period. The factors most closely associated with the occurrence of chronic bronchitis primarily include smoking, cigarette smoke, dust, and irritants such as sulfur dioxide, nitrogen dioxide, chlorine, ozone, etc. Additionally, some infectious factors may also be somewhat related to the occurrence of chronic bronchitis, with the most common possibly being infections by mycoplasma, bacteria, or viruses. Furthermore, chronic bronchitis may be related to age, climate, and other factors. Overall, the triggers of chronic bronchitis are not very clear at present, and it is advised to eliminate these risk factors as much as possible if present.