Millions of bacteria live in the mouth, particularly on the back of the tongue. In many people, they are the primary causes of bad breath. The mouth's warm, moist conditions are ideal for the growth of these bacteria. Most bad breath is caused by something in the mouth.

Symptoms

You may not always know that you have bad breath. That's because odor-detecting cells in the nose eventually get used to the smell. Other people may notice and react by stepping away from you as you speak, or making a face.

Other symptoms depend on the underlying cause of bad breath:

Infections in the mouth — Symptoms depend on the type of infection. They can include:

• Red or swollen gums that may bleed easily, especially after brushing or flossing
• Pus between teeth or a pocket of pus (abscess) at the base of a tooth
• Loose teeth or a change in how a denture fits
• Painful, open sores on the tongue or gums

Respiratory tract infections — Symptoms may include:

• Sore throat
• Swollen lymph nodes ("swollen glands") in the neck
• Fever
• Stuffy nose
• A greenish or yellowish discharge from the nose
• A cough that produces mucus

Dry mouth — Symptoms may include:

• Difficulty swallowing dry foods
• Difficulty speaking for a long time because of mouth dryness
• Burning in the mouth
• An unusually high number of cavities
• Dry eyes (in Sjögren's syndrome)

Illnesses — Symptoms of diabetes, lung disease, kidney failure or liver disease

Diagnosis

A dentist or physician may notice bad breath during an office visit. Sometimes, the smell of the patient's breath may suggest a likely cause for the problem. For example, "fruity" breath may be a sign of uncontrolled diabetes. A urine-like smell, especially in a person who is at high risk of kidney disease, can sometimes indicate kidney failure.

Your dentist will review your medical history for conditions that can cause bad breath and for medicines that can cause dry mouth. Your dentist also will ask you about your diet, personal habits (smoking, chewing tobacco) and any symptoms. He or she also will ask who noticed the bad breath and when.

Your dentist will examine your teeth, gums, mouth and salivary glands. He or she also will feel your head and neck and will evaluate your breath when you exhale from your nose and from your mouth.

Your dentist may refer you to your family physician if an illness is the most likely cause. In severe cases of gum disease, your dentist may suggest that you see a periodontist (dentist who specializes in gum problems).