There are a number of potential causes of bad breath. Some causes are related to their medical conditions such as Acid Reflux, tonsil infection, etc.
Smoking can cause bad breath as well. But the vast majority of cases of bad breath comes down to oral hygiene. We all have sulfur-producing bacteria in our mouth that breed beneath the surface of the tongue and often in the throat and tonsil areas.
Without proper oral care by regularly brushing and flossing our teeth, we let these foul odor producing bacteria feast on food particles and plaque buildup on the teeth and gums.
This plaque can also cause pockets of build-up between the teeth and gums, which could lead to gum disease such as periodontitis.