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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.
Causes of Bad Breath. Over 50 percent of adults complain of chronic bad breath, according to an article in The Journal of Dental Hygiene. Many times, the odor is a temporary occurrence caused by eating certain foods, like garlic, onions and certain spices. Consuming alcohol and smoking or chewing tobacco can also give your breath a foul odor. Preventing bad breath due to these kinds of external factors simply involves avoiding the offensive substance.