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1 Persistent bad breath or a bad taste in the mouth can also be one of the warning signs of gum disease; which is caused by plaque.  Dry mouth. This occurs when the flow of saliva decreases and can be caused by various medications, salivary gland problems or continuously breathing through the mouth.
About half the population suffers from bad breath caused by factors other than food, drinks and cigarettes. Of those, only about 10 percent come from other health issues such as diabetes, liver and kidney disease. The number of people who suffer from bad breath because of stomach problems is even lower.