Bad breath is often caused by bacteria living in your mouth. The bacteria feed off of carbohydrates in your diet, and as they flourish they produce odorous gases – this is what you are smelling when you smell bad breath. A dry mouth is another bad breath culprit. Alcohol, coffee, and prescription medication can dehydrate your mouth, giving bacteria a nice environment to grow in. Another cause is smoking, which leaves unpleasant carcinogenic particles in your throat and mouth. This is sometimes referred to as ‘smoker’s breath’.