Saliva helps to flush out the mouth and prevents bacteria from settling. Whereas dry mouth can help bacteria to breed. Similarly, gum disease can  cause bad breath due to putrefaction of bacteria in the mouth.

Obvious culprits are tobacco, alcohol, garlic and onions. So, give up smoking and drink alcohol in moderation. Gargle your mouth thoroughly after eating and drinking to prevent bad breath.

A low-carb diet makes your body burn stored fats for fuel instead of carbs. This can cause a condition known as ketosis  which can cause bad breath as foul-smelling ketones are released through the mouth.

GERD (gastro esophageal reflux disease) and diabetes are two illnesses that can cause bad breath. In fact, bad breath is one of the earliest symptoms of diabetes.