Halitosis, or bad breath, can have many causes. The most common cause of halitosis occurs in the mouth. Certain factors contribute to the mouth exuding a foul odor, including poor dental hygiene, tooth decay, and gum disease (gingivitis and periodontitis). Volatile sulfur compounds (VSCs), derived from bacterial plaque that thrives in the mucus of the mouth, have also been found to cause bad breath. Bacteria located upon the tongue are also a frequent source of halitosis, and may be the strongest determinant. 
Other risk factors that can cause halitosis include; nose or throat infection (such as sinusitis), postnasal drip, acid reflux, indigestion, constipation, insufficient friendly intestinal bacteria, an overabundance of unfriendly bacteria, intestinal toxins, and stomach gases. Bad breath is also frequently caused by eating foods with a strong, distinctive odor, such as garlic and onions. Underlying health conditions can cause halitosis include; lung disease (such as chronic lung infections, bronchiectasis or lung abscess), liver failure, kidney failure, and diabetes (ketoacidosis ‘fruity’ breath).
Along with the symptoms of an underlying disorder, the symptoms of halitosis may include:
- Foul odors coming from the mouth
- ‘Fishy’ breath odor may occur with liver failure
- ‘Urine-like’ breath odor may occur with kidney failure
- ‘Fruity’ breath odor (from acetone in the breath) may occur in diabetics developing ketoacidosis
If bad breath is caused by gum disease (gingivitis and periodontitis), symptoms may also include:
- Bad taste in mouth
- Swollen and/or recessed gums
- Hot and cold tooth sensitivity
- Gums bleed easily
- Loose teeth
According to the Centers for Disease Control:
- Periodontal (gum) disease is more common among diabetics.
- Young adults with diabetes have about twice the risk of getting periodontal disease than those without diabetes.
- About one-third diabetics have severe periodontal diseases, in which there is a loss of attachment of gums to the teeth measuring 5 millimeters or more. 
Halitosis, which comes directly from the mouth, can be treated by practicing a good oral hygiene regiment. This process includes the daily processes of tongue brushing and flossing. For the prevention of VSCs, dentists may provide patients with tongue scrapers and brushes to remove bacteria from the tongue’s crevices. Anti-inflammatory and antibacterial mouth rinses are also commonly prescribed. To further eliminate bad breath, certain foods that cause either halitosis, indigestion, allergies, or stomach gas, should be avoided when possible. Periodic dental visits are recommended to prevent, identify, and treat gum disease or tooth decay.
Halitosis caused by underlying conditions such as lung disease, liver failure, kidney failure, and diabetes must be identified through a complete diagnostic workup by a qualified health care professional, in order to render the appropriate treatment.
Probiotics (Lactobacillus acidophilus and Bifidobacteria) Probiotics including lactobacillus acidophilus (small bowel friendly bacteria) and bifidobacteria (large bowel friendly bacteria) are nutritional supplements containing the same beneficial bacteria that are found in the digestive tract. The supplementation of probiotics has been shown to enhance intestinal tract immunity and can be helpful for post-antibiotic therapy. When there an imbalance in the ratio of bad bacteria vs. friendly bacteria occurs, bad breath results. Probiotic supplementation may be helpful for halitosis therapy by maintaning a greater ratio of friendly bacteria over the harmful variety. [3, 4]
Psyllium and Pectin Fiber Psyllium and pectin fiber (fruit fiber) supplementation have been traditionally used as bulking agents to improve stool consistency, promote intestinal motility, and assist in the body’s natural detoxification processes. Because intestinal toxins have been shown to cause bad breath, the use of natural plant fibers such as pectin and psyllium may be helpful for halitosis therapy. 
Tea tree oil Tea tree oil, extracted from the leaves of the native Australian Melaleuca alternifolia tree, has been used for centuries as an antiseptic, antibacterial, antiviral, and antifungal agent. Studies report that tea tree oil is effective in treating a wide range of microbial infections, including oral bacteria that cause cavities, gum disease, and halitosis. Tea tree oil can be an effective addition to antiseptic oral rinses and toothpastes. [5, 8]
Vitamin C Vitamin C deficiency is the most prominent nutrient associated with mouth and gum disease. Studies have shown that Vitamin C supplementation prevents periodontal disease, supports healthy teeth and gums, enhances immunity, and has potent antioxidant and anti-inflammatory properties. Because excess toxins can cause bad breath, vitamin C supplementation is essential in the eradication of halitosis. [4, 9]
Chlorophyll (Vitamin K) Chlorophyll, a rich source of vitamin K, is found in alfalfa liquid, wheatgrass, and barley juice. Chlorophyll has potent antioxidant properties and neutralizes unpleasant odors, which may be an effective inclusion in one’s halitosis therapy. [4, 10]
Zinc Zinc deficiency is associated with mouth and gum disease. Studies have shown that zinc supplementation prevents plaque growth and periodontal disease, neutralizes VSCs, enhances immunity, and has potent antioxidant and anti-inflammatory properties. The combination of zinc supplementation and oral rinses containing zinc, can be effective in inhibiting plaque growth and preventing bad breath. [4, 11-14]
Green tea (Camellia sinensis) Green tea, derived from the leaves of the Camellia sinensis plant, possesses strong antioxidant properties. Studies suggest that green tea is effective in treating a wide range of microbial infections, including the oral bacteria that cause cavities, gum disease, and halitosis. Drinking green tea may even assist in destroying bacteria that could potentially cause bad breath. [15-17]
Bilberry (Vaccinium Myrtillus) Bilberry flavonoids (anthocyanosides) have potent antioxidant and anti-inflammatory effects and may help prevent mouth and gum disease . Both diseases are contributing factors to bad breath.
Vitamin A and Beta-Carotene Vitamin A deficiency is associated with mouth and gum disease. Vitamin A and beta-carotene supplementation enhances immunity, has potent antioxidant and anti-inflammatory properties, and can help prevent mouth and gum disease. Vitamin A may be helpful for halitosis therapy. [4, 18-19]
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