Recently, we found through patients and online consultation that many people still have a lot of ambiguity in their understanding of pulmonary fibrosis. Here, we would like to discuss how to correctly understand pulmonary fibrosis, so that the disease can be accurately diagnosed and reasonably treated, taking into account our clinical experience and several issues that are easily misunderstood. The term “pulmonary fibrosis” does not refer to an independent disease, but is a general term for a large group of diseases. Pulmonary fibrosis is medically classified as a diffuse interstitial lung disease (so-called interstitial lung disease), and in recent years it has also been called diffuse substantive lung disease. There are many causes of pulmonary fibrosis, the common ones being environmental, occupational, physical and chemical factors, such as asbestos, mineral dust, chemotherapy drugs, radiation damage, and inhalation of harmful gases. Exogenous allergic alveolitis caused by exposure to pigeon droppings, animal fur, moldy withers, etc. can also lead to pulmonary fibrosis. Some rheumatic immune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, dry syndrome, dermatomyositis, scleroderma, etc., can be accompanied by pulmonary fibrosis, and some pulmonary fibrosis even occurs before. For those with unknown causes, they are collectively referred to as idiopathic interstitial pneumonia, which includes what is often referred to as idiopathic pulmonary fibrosis. Only through multiple tests, combined with clinical manifestations, can a physician clarify exactly what type of pulmonary fibrosis belongs to and what may be the cause. Only when the diagnosis is clear can we talk about rational treatment. Question 2: Not all cases of pulmonary fibrosis are incurable. I often hear people say that “there is no cure for pulmonary fibrosis” or even “you can only live for 5 years at most”. This is a very incomplete and unscientific statement. If there is some truth to this view, I think it refers to the so-called “idiopathic pulmonary fibrosis”. Idiopathic pulmonary fibrosis is one of the many types of “pulmonary fibrosis” with unknown causes, and it has typical clinical manifestations and chest X-ray and CT features that are familiar to respiratory physicians. There is really no reliable drug treatment for this disease, and the disease tends to progress gradually, but the rate of disease progression is not the same for different patients. Clinical observations abroad have found that the median survival of patients is about 5 years, which is only a statistical figure; in fact many patients survive for much longer than 5 years! It should be specifically noted that the above recognition is limited to idiopathic pulmonary fibrosis! In fact, most cases of pulmonary fibrosis found in the clinic are not idiopathic pulmonary fibrosis, but secondary pulmonary fibrosis. After encountering pulmonary fibrosis, one of the most important tasks for the physician is to clarify whether it is idiopathic or secondary. For example, if it is clear that pulmonary fibrosis is caused by a rheumatic immune disease, the focus of treatment should be on the primary cause. Some pulmonary fibrosis caused by environmental factors can remain in a relatively stable state for a longer period of time after being removed from the corresponding environment. Question 3: Pulmonary fibrosis cannot be diagnosed comprehensively based on chest radiographs and CT alone The initial diagnosis of pulmonary fibrosis is made by chest radiographs and lung CT, but relying on these data alone does not provide a comprehensive understanding of the disease. Chest radiographs and lung CT are the most important first step in the diagnosis of pulmonary fibrosis/interstitial lung disease, and misdiagnosis can occur during this first step. In clinical practice, we have seen many cases of suspected interstitial lung disease because of “interstitial changes” on CT due to inadequate inspiration or breath-holding, or suspected “diffuse shadows” due to poor CT conditions. In addition, it is possible to undergo unnecessary ancillary tests. In fact, pulmonary fibrosis/interstitial lung disease is one of the more difficult diseases to diagnose in respiratory medicine, requiring not only the physician’s experience and knowledge of the disease, but also a variety of other ancillary tests (including laboratory tests), which must be reasonable and accurate in order to make a comprehensive analysis of the disease and finally make a correct diagnosis. There are many ancillary tests mentioned above, including pulmonary function tests, various blood tests, bronchoscopy-related tests, and even lung biopsy. For these reasons, it is usually recommended that patients initially diagnosed with pulmonary fibrosis/interstitial lung disease should go to a respiratory department of a major hospital with the appropriate clinical experience and tests to further confirm the diagnosis and avoid misdiagnosis and mistreatment.