There are many reasons why there are cavities in the lungs but nothing is wrong with the condition, which may be caused by tuberculosis, lung abscess, lung cancer, and so on. 1. Tuberculosis: caseous necrotic material is discharged through bronchial tubes, and then air enters into the diseased tissue through bronchial tubes, and cavities are formed. 2. Lung abscess: suppurative infected tissues are discharged through bronchial tubes, and then gas enters into the diseased tissues, forming cavities with fluid level. 3. Lung cancer: the tumor tissue grows relatively fast, the central part is ischemic and hypoxic necrosis, the air enters into the necrotic tissue, forming a cavity with back wall and irregular inner wall. There are cavities in the lungs, but there may be other reasons. It is recommended to go to the hospital in time, improve the examination and carry out standardized treatment under the guidance of doctors.