Bronchitis is a lung disease in which there is increased secretion of mucus from the bronchi and trachea, and the cause is mainly due to infectious and non-infectious factors. People who smoke are much more likely to develop bronchitis than those who do not smoke. Bronchitis can be divided into acute bronchitis and chronic bronchitis. The clinical symptoms of bronchitis are: (1) cough, which is acute and usually presents as a dry cough that causes pain in the sternum if it is too frequent; (2) coughing up sputum, which is mostly white foamy mucus; (3) shortness of breath, which is common in the acute phase. Bronchitis can also be accompanied by systemic symptoms, such as fever and headache, but they last for a relatively short time. Tracheomalacia has a long and slow duration, with mild symptoms in the early stages, usually without obvious symptoms; in the late stages, it affects health and lung function. The lungs are not abnormal on auscultation in the early stages, or coarse breath sounds may be heard, and scattered dry and wet rales may be heard as the disease gradually progresses. Laboratory tests for white blood cell counts are usually normal, and chest x-rays are more diagnostic. It is important to pay attention to prevention in daily life, to exercise properly, to strengthen the immune system, to avoid excessive temperature differences between indoors and outdoors, which can lead to colds, and to quit the habit of smoking, as smoking is an important cause of the disease.