Bad breath is also called halitosis. It is caused by anaerobic sulfur producing bacteria which normally live within the surface of the tongue and in the throat. Bad breath can be transitory or chronic.
Transitory halitosis is caused by foods such as garlic and onions. This odor actually originates in the lungs, and generally only lasts from 24 to 72 hours. Another major cause of transitory halitosis is cigarette smoking. A smoker's breath smells because of tar, nicotine, and other noxious substances accumulating on the teeth, tongue, cheeks and other soft tissue. Smoking dries the membranes of the mouth, and the amount of saliva. Less saliva means less oxygen or an anaerobic environment which is perfect for sulfur-producing bacteria.
Chronic halitosis does not improve over time. The odor of chronic halitosis emerges when bacteria in the mouth, and on the teeth and tongue cause the formation of volatile sulfur compounds, in the form of hydrogen sulfides. These compounds produce a strong "rotten egg" smell. This is a long-term problem that requires professional treatment.
About 85% of halitosis is linked to dental causes, while the rest linked to medical causes.
Dental causes include:
- Extensive dental decay.
- Periodontal (gum) disease.
- Oral infections or abscesses.
- Oral cancers.
- Dry mouth condition (Xerostomia). Many medications can contribute to Dry mouth.
- Oral conditions resulting from post-nasal drips or discharges.
- A growth and multiplication of specific types of anaerobic bacteria.
Medical causes include:
- Sinus infections & abnormal sinus anatomies, post nasal drainage (drips)
- Tonsilar infections or tonsiloliths
- Lung diseases
- Kidney diseases
- Liver diseases
- Diabetes
- Gallbladder dysfunction
- Menstruation
- Carcinomas
- Certain foods
When a medical condition is suspected, patients are advised to consult with their family physician.
Some common treatments for bad breath have been through the use of mouthwashes, mints, and gums to cover up odors, but they have not been effective in treating halitosis. Some of these remedies can actually worsen a bad breath condition.
Although there is hardly complete cure for the cause of 90% of chronic halitosis, your dentist can help diagnose the various types and causes of halitosis, and the problem can be more effectively managed.
Treatment 
Who Has the Bad Breath Problem? What are the Symptoms?