Bacterial buildup on the teeth and gums, chronic sinus infections, kidney disease and diabetes are all potential causes for mothball breath, according to WebMD and Allnurses. Anorexia is also known to produce odd and foul-smelling odors in the mouth that are akin to the smell of mothballs.
The most common causes of mouth odor are poor dental hygiene, gum disease or unclean dentures, according to WebMD. Diet and medicines can also be contributing factors. Chronic dry mouth caused by acid reflux and postnasal drip are also common causes of bad breath. Other internal medical causes include liver disease and chronic bronchitis.