The etiology of chronic bronchitis is not very clear at present. It is considered that many factors work over a long period to cause chronic bronchitis. The most common factors include long-term irritation from harmful gases and particles, such as cigarette smoke, smog, dust, irritating gases like sulfur dioxide, nitrogen dioxide, etc., as well as infectious factors. There might also be a certain relationship with the occurrence of chronic bronchitis, but so far, no close relationship has been found between chronic bronchitis and genetics, and there is no evidence to prove that chronic bronchitis is a hereditary disease.