Cigarette smoke is a complex mixture, and as of 1988 as many as 5068 chemical components have been identified in smoke. Smoking is a multifaceted threat to human health, and can cause damage to many organs and systems throughout the body, especially to the lungs. Smoking can cause not only COPD and lung cancer, but also interstitial lung disease. Smoking is the most important environmental risk factor for COPD. As a result of years of smoking, one quarter of smokers gradually develop shortness of breath after activity, dyspnea, loss of work capacity, reduced quality of life, and eventually COPD. Some patients who are short of breath when walking up stairs or climbing hills often think it is their age or lack of exercise, ignoring the damage tobacco does to their lungs, and do not go to the hospital until their lung function is severely diminished, by which time smoking has caused irreversible damage to their lungs. It is important to note that the more you smoke, the younger you start smoking, the longer you smoke, and the deeper you inhale smoke when you smoke, the greater your risk of developing COPD. The high incidence and mortality of lung cancer has become a global concern, and according to the Beijing Center for Disease Control, the leading disease causing death among Beijing residents in 2007 was lung cancer. It is well known that smoking is one of the main causes of lung cancer. 90% of lung cancers are related to smoking, and more than 60 kinds of cigarette smoke are recognized as carcinogens, mainly including nicotine, tobacco tar, carbon monoxide, hydrocyanic acid, ammonia and aromatic compounds. If you smoke more than 25 cigarettes a day, 12% of smokers may develop lung cancer. In recent years, it has been found that smoking can also cause a number of interstitial lung diseases. Respiratory bronchitis, once called “smoker’s bronchitis,” is a disease that differs from what is often called “chronic bronchitis” in that the damage is done to the very small terminal and respiratory bronchioles. In asymptomatic smokers, bronchitis is usually already present in the lungs. When viewed under a microscope, the lumen of the respiratory bronchioles is full of alveolar macrophages that have engulfed soot particles, called “smoker’s macrophages”. This chronic inflammation of the small bronchioles persists even years after smoking cessation. In some patients, bronchiectasis spreads to the alveoli and interstitium, with interstitial pneumonia and pulmonary fibrosis. These patients present with shortness of breath and cough, which are often misdiagnosed as chronic bronchitis combined with pneumonia and treated repeatedly with antibiotics, but the dyspnea remains unrelieved. The vast majority of patients and even respiratory specialists were still quite unfamiliar with desquamative interstitial pneumonia. It was not until the 1990s that the medical community developed a more uniform understanding of this disease. Most cases of desquamative interstitial pneumonia are seen in chronic smokers, who gradually develop dyspnea and shortness of breath after activity, with a high-resolution CT of the chest showing ground glass shadows in both lungs with pulmonary fibrosis. If not diagnosed and treated promptly, desquamative interstitial pneumonia can lead to fibrosis of both lungs, and the patient’s lungs gradually lose their ability to ventilate and exchange gases. Pulmonary Langerhans cell histiocytosis is also a lung disease that occurs in smokers and is more prevalent in younger people. The clinical presentation varies from patient to patient, and some smokers have no respiratory symptoms, making it easy to miss the diagnosis, and it is detected during routine physical examinations or when the disease is more severe with dry cough and dyspnea after activity. In patients with pulmonary Langerhans cell histiocytosis, nodules and cystic cavities in both upper lungs can be seen on chest radiographs or high-resolution CT of the chest. In some patients, spontaneous pneumothorax due to rupture of the subpleural cystic cavity is detected at the time of presentation. In addition, idiopathic pulmonary fibrosis is a lethal lung disease that occurs in middle-aged and elderly people, and smokers are at a significantly increased risk of developing this disease. In conclusion, the risks of tobacco to the lungs cannot be ignored, and staying away from tobacco can prevent or greatly reduce the occurrence of these diseases. Once smoking-related lung disease is detected, timely cessation of smoking can “mend the fold”. Some diseases, such as respiratory bronchitis and pulmonary Langerhans cell histiocytosis, may disappear spontaneously after quitting smoking. Let’s get rid of tobacco and really breathe easy.