Bad breath from the stomach can be caused by a variety of factors related to the digestive system. Here are some of the most common causes:

• Gastroesophageal reflux disease (GERD): This is a digestive disorder where stomach acid flows back into the esophagus, causing heartburn and sometimes bad breath.

• H. Pylori infection: This is a type of bacteria that can cause stomach ulcers and other digestive problems, including bad breath.

• Kidney disease: Chronic renal disease can sometimes cause bad breath that smells fishy or strongly like ammonia.

• Small Intestinal Bacterial Overgrowth (SIBO): This is a condition where there is an overgrowth of bacteria in the small intestine, which can cause digestive symptoms and bad breath.

• Digestive system infection: Certain digestive system infections, such as giardiasis, can cause bad breath.

Its important to note that bad breath from the stomach can be more difficult to identify and treat than regular bad breath, so its important to consult a healthcare professional if you suspect that your bad breath is related to a digestive issue.