Bad breath also known as halitosis can result from poor dental health habits and may be a sign of other health problems such as dry mouth, pneumonia, bronchitis, chronic sinus infections, diabetes, liver and kidney problems. If you don't brush your teeth daily, food particles remain in your mouth and cause bacterial growth between teeth, around the gums and on the tongue, which causes bad breath. Smoking or chewing tobacco-based products can also cause bad breath, stain teeth and irritate the gums.
Attribution: Straight Talk Foundation