Persistent bad breath may be due to a treatable dental problem, such as an undiagnosed cavity or periodontal (gum) disease. Sometimes a broken filling can trap food particles. If you visit the dentist and no such problem is found, however, you may want to investigate further and talk to your physician about other possible causes. Occasionally, ongoing bad breath is due to something in the respiratory tract (such as a sinus or lung infection) or gastrointestinal tract or to a systemic (body-wide) condition. Diabetes, for example, can give the breath an unpleasant chemical smell.
Of course, what you eat can contribute to bad breath, too. Certain food items have a very pungent smell and when you eat them, you end up getting a bad odor in your mouth. The foods and drinks that come under this category are garlic, onions, cheese, orange juice, soda, etc. When you eat or drink any of these, the oils present in them get carried to your lungs. Ultimately, they come out through your mouth. The result is bad breath. Another big loser when it comes to turning your breath sour, and harming your health, is tobacco.