Bad breath is not necessarily a precursor of cancer. Although some tumor patients have heavy breath, for example, stomach cancer patients often have smelly duck egg-like breath, lung cancer patients have putrid breath, and tongue cancer, nasopharyngeal cancer, laryngeal cancer and other oral and head and facial tumor patients have very serious bad breath. However, the most common cause of bad breath is oral diseases, such as gingivitis, periodontitis, dental caries, etc. In addition, some systemic diseases can also cause bad breath. In addition, some systemic diseases can also cause bad breath, for example, peptic ulcers, chronic gastritis and other diseases can lead to sour breath smell. The breath of diabetic patients occasionally tastes like rotten apples. Patients with chronic renal insufficiency and renal failure have an earthy taste in their mouth. Therefore, if you have bad breath, don’t think of having cancer first, but go to the hospital for an examination to clarify the cause of bad breath and don’t scare yourself.