What are the causes of crackles in the lungs?

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Crackling in the lungs can signal a variety of lung diseases. Although usually too quiet to hear without the aid of a stethoscope, crackling may sound like rattling or the crumpling of paper in the chest. In many of these diseases, the crackling is a result of the rapid opening of the lungs' air sacs.

Although crackling itself is not dangerous, it can be a symptom of dangerous diseases, as well as more harmless conditions.


Pneumonia is one of the most common of all lung diseases and is caused by a viral or bacterial infection of the lungs. The infection can cause the air sacs in the lungs, called alveoli, to open. This causes a characteristic crackling noise. However, crackling in the lungs due to pneumonia may only be heard upon medical examination with a stethoscope.


Bronchitis is a family of conditions in which the mucous membranes of the lungs become inflamed. This can be caused by various environmental factors, including viruses, bacteria, smoking and inhalation of polluted air. Bronchitis can cause a crackling sound in the lungs, often accompanied by other abnormal sounds, such as bubbling. Bronchitis should be treated by a doctor immediately.

Pulmonary fibrosis

Pulmonary fibrosis is a condition caused by abnormal growth of fibrous tissue in the lungs. Pulmonary fibrosis may arise without any cause at all, or it can be caused by the inhalation of pollutants in the air. Crackles can often be heard at the end of a breath in people who have pulmonary fibrosis. Other symptoms of pulmonary fibrosis include chest discomfort, shortness of breath, and persistent fatigue.

Pulmonary oedema

Pulmonary oedema is a build-up of a fluid in the lungs, caused by the circulatory system's inability to clear it out. Crackling sounds in the lungs are common in patients with pulmonary oedema, along with coughing, shortness of breath and excessive sweating. Pulmonary oedema is often caused by heart problems such as congestive heart failure. Pulmonary oedema can be fatal if left untreated, as it restricts oxygen flow to the rest of the body.