There are a number of causes of bad breath, foremost among them being bacteria in the mouth, stomach and intestinal disturbances, bowel sluggishness, sinus or throat infections, and tobacco and alcohol use. Stress is another cause which may not be readily apparent when you are looking for reasons for bad breath.
Stress affects the digestive system.
An insufficient supply of digestive enzymes may be another cause. Other sources of bad breath are in the nose and the nasopharynx, the area above the base of your tongue. Bad breath may emanate from the back of the throat due to sinus or tonsil infections resulting in excess bacteria. See Sinus Problems in our Ailments section for more information. If you have sinus or throat problems you may well have some form of allergy.