To determine whether it is bad breath or bad stomach odor, you can consider paying attention to the following points, such as cleaning the mouth and doing a gastrointestinal examination. 1. Cleaning the oral cavity: you can clean the oral cavity first, if the bad breath disappears after cleaning, it may be halitosis, if it still does not disappear after cleaning, it may be stomach odor. 2. Check the oral cavity: when the microbial environment of the oral cavity is damaged, it may cause bad breath, and there are often some oral diseases, such as periodontitis, dental caries, etc. It is recommended to go to the stomatology department, and a professional doctor will conduct a detailed oral examination to obtain the relevant diagnosis. 3. Check gastrointestinal: stomach odor is mainly caused by Helicobacter pylori infection, often accompanied by some gastrointestinal diseases, such as gastritis, at this time you need to go to the gastroenterology department to carry out relevant examinations, such as Helicobacter pylori test, gastroscopy.