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Bad Breath - What Causes A Bad Smell in The Mouth?

Updated: Nov 19

Bad breath, also known as halitosis, may at first glance seem like a very random unimportant topic to address. However, dating back as early as 400 BC humans have used scent to help detect human diseases.[1] Certain conditions can lead to a change in a person’s breath, for example:

  • Kidney disease causes urea levels to rise, which is off-gassed as ammonia in the breath (urine-scented)

  • A person with a small intestinal bacterial overgrowth has extra methane and hydrogen sulfide in their breath (egg smell)

  • Low-carb diets can cause ketosis which causes acetone-scented breath (somewhat fruity or like polish-remover)

  • Stomach infection with H. Pylori increases ammonia and hydrogen sulfide levels in the breath (egg or urine-scented breath)

  • Liver disease can make it so the liver can't filter certain toxic substances from your blood anymore. These substances build up in the blood and come out in the breath


There are over 1000 different compounds that studies have identified in the breath of humans. Medicine uses breath to diagnose many types of diseases.


Tonsillitis

Tonsillitis can cause bad breath. There may be white discharge on the tonsils when this happens (not always however). This white buildup on the tonsils can eventually form tonsil stones if left untreated. These can worsen bad breath and tend to contain a buildup of bacteria.


Tonsillitis itself can then be related to many underlying imbalances in the body. For example, a 2023 study found that tonsillitis is about twice as common in those with low levels of vitamin D.[2] Furthermore, vitamin D deficiencies were present in the majority of those with tonsillitis. At our clinic we complete a tonsillitis blood test panel of eight or more items (depending on your case) to screen for tonsillitis risk factors. You can read more about our approach to tonsillitis here.


Dry Mouth

For dry mouth sufferers, unpleasant breath can be a common side effect. Dry mouth is associated with halitosis, as the lack of salivary flow compromises the antibiotic action of the saliva, leading to more bacteria within the mouth and increased plaque on the teeth and coating on the tongue. Saliva also helps to wash away particles that may cause bad breath.


Medications Related to Dry Mouth

Certain categories of medications can lead to dry mouth, including diuretics, antihistamines and decongestants, tricyclic antidepressants, and amphetamines.


Autoimmune Causes of Dry Mouth

Certain autoimmune diseases can affect the salivary glands and lead to dry mouth. For example, Sjogren’s syndrome affects the body’s ability to produce saliva readily, making the mouth feel chalky or cotton-like. It tends to cause significant dry mouth.


Nasal (Nose) Related Causes

If the halitosis is related to the nose, then the odor usually smells the greatest with breathing through the nose instead of the mouth. Nasal related causes of halitosis include:

  • Acute or chronic sinusitis

  • Postnasal drip, which can cause bad breath if the drip is putrefied by the tongue microbiota

  • Foreign bodies in the nose, usually seen in children, which are an uncommon cause of halitosis


Nutritional Causes of Bad Breath

If others find that your breath is actually quite pleasant and not as bad as you note - then this could be a sign of a nutritional deficiency. A 2024 study found that low levels of zinc may lead to a strange flavor in the mouth, giving the perception of bad breath.


Respiratory Causes Bad Breath

Certain lung infections may lead to halitosis. This includes bronchitis, bronchiectasis, or lung abscess.


Digestive Causes of Bad Breath

Compounds with scent from the digestion can be released from the stomach through the esophagus and the mouth and cause bad breath. Some examples include:

  • Gastroesophageal reflux disease

  • Helicobacter pylori infection

  • Small intestinal bacterial overgrowth


Systemic Causes of Bad Breath

With systemic causes of halitosis, the intensity of the odor from the mouth and the nose is similar. Some examples include:

  • Advanced kidney disease

  • Advanced liver disease

  • Diabetic ketoacidosis

  • Trimethylaminuria, a rare genetic condition characterized by a fishy odor in breath, sweat, and urine


Food Related Causes

This may be stating the obvious, but coffee, alcohol, garlic, onions, and smoking can all cause bad breath. Garlic can last for at least 24 hours.


Dental-Related Causes

This can often be checked with a dentist. Cavities, gingivitis (inflammation of the gums), periodontitis and foods stuck in teeth can cause bad breath. At our clinic we run a gingivitis/periodontitis blood testing panel that can test for 15 items that studies have found are related to these conditions. You can read more about this here.


Cancer-Related

A 2020 study found that certain cancers may lead to distinct changes to the breath, for example there are twenty-two compounds that five studies have identified that are unique to those with head and neck cancers. That being said, cancer is an extremely rare cause of bad breath.


Lifestyle Factors

Addressing the root cause to bad breath is likely the best approach, however some things that may help in the meantime are:

  • Sugar-free chewing gums (which stimulate saliva production).

  • Good hydration.

  • Decreasing alcohol and coffee intake.

  • Proper dental care and oral hygiene, including daily flossing.

  • Gentle cleaning of the posterior portion of the tongue dorsum (eg, with a plastic tongue cleaner).

  • Rinsing and gargling with a mouthwash before bedtime.


Natural Therapies for Bad Breath/Halitosis

The therapies used will depend on what these blood testing panels have found. After identifying what issues may be present, they can be addressed through diet, supplementation, lifestyle or medication. Our clinic will use a combination of therapies tailored to what your results show.


Conclusion

Before initiating any treatment, it's crucial to first conduct comprehensive testing to identify any underlying imbalances. This testing helps ensure that the appropriate treatments are chosen and that the correct dosage is administered. Addressing a deficiency without proper diagnosis could lead to unintended side effects.


Halitosis can be related to many underlying factors. At our clinic, we have a list of over 30 nutritional, hormonal, immunological, inflammatory, and metabolic factors related to halitosis that we can test for. Our approach includes thorough blood and breath testing, dietary evaluations, and personalized therapies to target the root causes of halitosis, to promote long lasting fresh breath!


References

[1] Nuwan Dharmawardana, Charmaine Woods, David I. Watson, Roger Yazbeck, Eng H. Ooi, A review of breath analysis techniques in head and neck cancer, Oral Oncology, Volume 104, 2020, 104654, ISSN 1368-8375, https://doi.org/10.1016/j.oraloncology.2020.104654.

[2] Shrestha D, Bista M. Association Between Vitamin D Deficiency and Recurrent Tonsillitis. J Nepal Health Res Counc. 2023 Mar 10;20(3):731-733. doi: 10.33314/jnhrc.v20i3.4223. PMID: 36974865.

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