Here are the most frequent causes of bad mouth smell

Stomatitis This is an inflammatory process in oral mucosa caused by staphylococcus, streptococcus, or fungal infection. Typical symptoms include swelling and redness of the mucous membrane, the appearance of a whitish plaque, and multiple ulcers on the inner surface of the cheeks, under the tongue, or on the palate. A dental practitioner will prescribe an appropriate treatment that could help eliminate this problem in several days, in most cases.

Gastrointestinal disorders Patients with gastritis, pancreatitis, or reduced tone of the sphincter between the stomach and esophagus can sense the taste of undigested food, bitterness, or another unpleasant taste, accompanied by a corresponding smell. Such patients should consult a gastroenterologist.

Diabetes The smell of acetone in the breath is considered a clear symptom of diabetes. The doctors call this condition ketoacidosis, which happens with both diabetes type 1 and type 2. The body of the patient with diabetes cannot break down lipids, which leads to the formation of toxic substances. Meanwhile, the smell of acetone can happen in those who overeat carbohydrates or are deficient in them.

Liver disorders Hepatitis, cholecystitis, or gallstone disease can show up in the form of a bitter taste in the mouth, which doesn't disappear after brushing the teeth or using a breath freshener. Any food would have the same bitter taste while the patient's breath smells like bile. It can also happen in the absence of serious pathologies, for example, when overeating fatty foods or in case of bile stagnation in the bile ducts.

Fresh green tea—about one and a half liters per day—can be an effective home remedy. If the bitterness and bad smell do not disappear in 24 hours after drinking a sufficient amount of green tea, you should see a hepatologist.

Inflammatory processes of respiratory organs Tonsillitis, sinusitis, and frontal sinusitis are often associated with the smell of pus when exhaling air both through the mouth and nose. Such patients need to consult an otolaryngologist, especially if other symptoms include difficulty breathing and pain in corresponding areas, raised body temperature, and feeling unwell.

Acute and chronic renal failure When kidneys lose function, the products of metabolism are not entirely excreted with urine. The toxic substances enter the blood flow and are evaporated by the respiratory organs, making the exhaled air smell like kidneys.

It is a very dangerous health condition that calls for immediate assistance by a nephrologist. If you experience bad breath that doesn't disappear in 24 hours, you should consult with a general practitioner who will refer you to another medical professional for diagnostics.

23 March 2021