Diet, Illness, and Medications
There are some potential causes of bad breath that aren’t related to oral bacteria. For example, if you are on a low-carb diet, your body enters a metabolic state called ketosis, which increases the concentration of ketones in your breath, which can make it smell unpleasant.
Diabetes can lead to bad breath, too, as well as some other illnesses, such as gastroesophageal reflux disease (GERD). In rare cases, bad breath may be linked to cancer.
Some medications can cause bad breath. Usually, this is because they lead to dry mouth, but sometimes it’s related to the breakdown of the chemicals.