Bad breath from the stomach is extremely rare. So rare, that of the thousands of people whom our team has smelled professionally, we cannot recall even one case in which the stomach appeared to be clearly involved. The esophagus, which connects the stomach with the mouth, is a collapsed tube, not an open one. Each chunk of food (called a bolus) moves down the esophagus similar to the way that a swallowed frog moves down a snake. Similarly, when one belches, a little bubble of air moves up the esophagus and exits at the mouth. We are not trying to argue that belches don't smell. They can and do. It's just that belching is a once-in-a-while phenomenon. The rest of the time, the esophagus closes off the stomach, so there is no continuous flow of air to the mouth.

Some people think that the tongue and stomach are connected, perhaps through reflux of liquid. Although I cannot completely rule that possibility out, the smell of tongues has only little in common with stomach odors. Furthermore, bad breath can usually be controlled by treatments limited to the mouth itself – which shows that the stomach has nothing or very little to do with the problem.

From my experience, when bad breath strikes, the stomach is the last place to look for an answer. In my opinion, a gastroenterologist who performs a gastroscopy (sticking a disgusting tube all the way down into your stomach to see what is going on) when a patient complains solely of bad breath, instead of first sending the patient to a dentist and otolaryngologist, is not practicing good medicine.

Some gastroenterologists (or other physicians) might prescribe antibiotics against Helicobacter pylori, which can cause stomach ulcers. The antibiotics, in such cases, will not only affect the stomach, but also have an effect on the oral bacteria – which might mislead to think that the cause for the malodor is gastrointestinal. In most cases, the odor will come back after a few weeks, as the oral bacterial populations recover.

The above notwithstanding, both Islamic and Jewish teachings mention the stomach as being involved in bad breath. In the Talmud, it is taught not to indulge in eating raw peas (again, the exact type of pea is unclear). Similarly, the ancient sage Rashi recommended that one walk a little following the meal, in order to prevent bad breath. We cannot rule out the possibility that in ancient times, some foods or habits (perhaps eating in a supine position) were more likely to result in continuous belching. And then again - perhaps the ancient religious lore is responsible for the common misconception that bad breath is primarily a stomach thing.