Bad breath should be firstly referred to dentistry and further examination should be done in general internal medicine or respiratory medicine. The cause of bad breath should be identified first, and the first visit should be made to the stomatology department, because bad breath is mostly caused by poor oral hygiene or oral diseases. If you do not brush your teeth in time after eating, food residue or soft scale will accumulate around the gum margin or become embedded in the gap between teeth, and the gum tissue will become red, swollen and bleeding due to long-term stimulation, leading to gingivitis, which will have bad breath, and this situation can be improved by scaling in periodontology. If the bad breath is caused by pulp necrosis due to tooth decay, and the unique odor of dead pulp teeth appears, this situation requires dental treatment, and you can register for consultation at the Department of Endodontics. Bad breath may also be caused by papillitis of the tongue, which requires a visit to the mucosal unit. In addition, bad breath can also be caused by digestive disorders of the gastrointestinal tract, or food that is not completely broken down in the stomach, resulting in a putrid odor, which requires a comprehensive internal medicine examination. If it is caused by pneumonia or endobronchial pneumonia and bad breath occurs during breathing, a consultation with respiratory medicine is required. Therefore, bad breath of carious origin should be referred to stomatology, while bad breath of gastrointestinal or respiratory origin should be referred to general internal medicine or respiratory medicine.