The most common cause of bad breath is the food you eat. Garlic, onions, some kinds of fish, and diets rich in fat and meat can all result in halitosis. When these foods are digested, volatile substances or chemicals are absorbed into your bloodstream and are carried to your lungs where they are exhaled in your breath. In one study, rubbing garlic on the feet actually caused bad breath!
The breakdown products of proteins in the body used for energy are exhaled through the lungs, and therefore missing meals, hunger, fasting, starvation, and low-calorie diets can also cause "hunger breath."
Because there is no flow of saliva during sleep, putrefaction (decomposition or rotting) of saliva and debris in the mouth can lead to bad breath in the morning.
Halitosis is also caused by:
- periodontal or gum disease that causes teeth to become loose, thereby creating pockets in the gums that harbour bacteria and lead to bad breath
- chronic lung or sinus infections
- breathing through your mouth because of enlarged tonsils or adenoids
- mouth infections such as thrush (candidiasis)
- systemic diseases such as diabetes, liver disease, or kidney disorders
- not brushing or flossing regularly
Taking certain medications can also cause bad breath, especially those that reduce the flow of saliva and dry out the mouth (e.g., some antidepressants, antipsychotics, antihistamines, decongestants, and medications to reduce high blood pressure).