What is bad breath?

Bad breath (aka halitosis or oral malodor) describes foul-smelling breath from the mouth. No surprises there.

Oral cause of bad breath is caused by bacteria (gram-negative anaerobes). These bacteria break down sulphur-containing amino acids and produce volatile sulphur compounds (VSCs). These bad-smelling compounds include hydrogen sulfide, methyl mercaptan and dimethyl sulfide.

It is the 3rd most common dental concern after cavities and gum disease. It is noted in 30-50% of the population as per some studies.

Bad breath can have serious consequences! It can hinder physical, social and psychological well-being. It can also impair future growth in career or academics.

Studies have shown that about 85-90% of halitosis is caused by oral factors and 8% are from beyond the mouth. The remaining cases do not have a known cause.

What are the oral causes of bad breath?

1. White coating on tongue

The most common factor of oral bad breath is thick white coating on the tongue! This is remaining bacteria and food on the tongue. It is similar to plaque on our teeth and is easily removable with a tongue cleaner!

2. Poor Oral Hygiene

Poor oral hygiene (brushing, flossing, tongue cleaning) can lead to bacterial growth which can lead to more VSCs being released.

Braces, dentures or other appliances should be cleaned routinely to minimize bacterial presence.

3. Dry mouth (dehydration or mouth breathing)

Dry mouth means low saliva flow. Saliva has natural anti-bacterial properties and washes away food. So when saliva decreases, bacteria flourish.

Dry mouth can be caused by dehydration or mouth breathing. Skipping meals can also lead to dry mouth as salivary flow usually increases when you eat. So don’t skip breakfast!

4. Dental disease (cavities, gum disease or infections)

Dental cavities, gum disease and dental infections are caused by bacteria and poor oral hygiene. Thus, it is important to have regular dental check-ups, cleanings and fix your cavities!

5. Diet

Pungent foods such as onion or garlic can cause bad breath after a meal. It is important to brush, rinse and clean your tongue after eating these foods.

Coffee and alcohol can also lead to bad breath as they cause dehydration and dry out the mouth in addition to having their own unique aroma.

Fish is also another food that can lead to a “fishy smell” after a meal. The American Society of Nutrition states the “fishy smell” is due to trimethylamine (TMA).

6. Tobacco or Vaping

Tobacco products (cigarettes, cigars, chewless tobacco) have their own aromas that can lead to bad breath.

Vaping and smoking (cigarettes or cigars) also can dry out the mouth causing reduced salivary flow which can cause more anaerobic bacteria to flourish.

What are non-oral causes of bad breath?

Non-oral causes of bad breath account for around 8% of cases. Examples are stated below:

• Non-oral causes of bad breath
  • tonsillitis
  • tonsil stones
  • sinusitis
  • post-nasal drip
  • throat infections (ex. strep throat)
  • foreign body in nose/oral cavity

These are due to bacterial infections or high bacterial presence in the nose, sinus or throat areas leading to bad breath coming from the mouth.

Medical conditions have been associated with bad breath per John Hopkins Hospital and the Cleveland Clinic.

• Medical causes of bad breath
  • heartburn/acid reflux
  • diabetes
  • liver disease
  • kidney disease
  • digestive disorders
  • head and neck cancer

The above non-oral and medical conditions are far less common than oral causes. These causes should be addressed with your medical provider.

How does “morning breath” happen?

Morning breath is bad breath noticed once you wake up! This is because 2 things happen while you sleep: 1) saliva flow decreases and 2) mouth breathing is more common.

Mouth breathing at night can further dry out your mouth which allows bacteria to grow.

This is why it is important to brush, floss and clean your tongue before going to bed. You are removing the bacteria before your saliva flow drops overnight. There may still be morning breath when you wake up but it will be less severe!

How do I prevent or treat bad breath in my child?

1. Clean your tongue, clean your tongue, clean your tongue!

Tongue cleaning is the #1 thing you can do to remove bacteria, food and old cells from your mouth.

There are different types of tongue cleaners and the right type may take a few tries to figure out for your own comfort zone. Tongue cleaners will be more effective than cleaning your tongue with a toothbrush.

Ideally, tongue scraping should be done in the morning (morning breath) and at night after your last meal. Try to get the back of the tongue (without gagging yourself) and be gentle!

• Tips on tongue cleaning
  • Use one appropriate to your mouth and tongue size
  • Scrape from back to front
  • Scrape as far back as possible without gagging yourself
  • Use firm pressure
  • Use multiple strokes to remove the white coating if needed
  • Clean your scraper after
    • Use an antibacterial rinse, especially if plastic

This WikiHow article is helpful for those who want more details on how to clean their tongue.

Metal/stainless steel tongue scrapers last longer than plastic ones and can more easily be cleaned. Plastic ones will need to be replaced after a few weeks-months depending on their condition.

Click on the photos below for links to Amazon. The right one for you may take some trial and error.

2. Good Oral Hygiene

Brush and floss regularly can reduce the amount of bacteria around your teeth. If you have braces or other dental appliances (dentures, implants or crowns), then make sure you are cleaning them routinely. See your dental hygienist as well for regular cleanings and advice to improve you oral hygiene!

Mouth wash can help as well! However, it is best to avoid mouth washes in children due to swallowing risk.

3. Avoid dry mouth

Dry mouth can firstly be addressed through regular hydration and eating routine meals. This will promote saliva flow, which will wash away bacteria.

After that, you can try regular chewing gum (sugar-free ideally), salivary substitutes or stimulants. Generally these are not recommended for children.

Mouth breathing is commonly due to nasal obstruction and is treated with tonsil/adenoid surgery. However, bad breath alone is not an indication for surgery. Instead, you should focus on easier remedies as stated in this section. Check out our previous Dentopedia mouth breathing post to learn more!

4. Diet

Avoid pungent smelling foods (garlic, onions, fish) or drinks that can dry out your mouth (caffeine or alcohol). Don’t forget hydration of course.

5. Routine dental care!

Dental care can address any areas of poor oral hygiene. Routine cleanings can remove bacteria that is tough to remove at home. Your dentist can treat your cavities, gum disease and any infections!

6. Avoid tobacco products and vaping

The final word…

Bad breath is caused by bacteria and food left behind in the mouth. Recommendations focus on improving oral hygiene with a strong emphasis on tongue cleaning. Lifestyle changes include dietary modification and avoiding tobacco/vaping products to prevent dry mouth. Non-oral causes are less common and can be addressed with a medical provider. It’s important to address bad breath with your dentist and dental hygienist if you are concerned!

References:

American Society for Nutrition. Is fish smelly?. (2011, August 24). https://nutrition.org/is-fish-smelly/

Aljudaibi R, Mubaraki S, Baseer MA. Parental Perception of Oral Halitosis in Their Children and Its Effect on Oral Health-Related Quality of Life: A Cross-Sectional Study. Patient Prefer Adherence. 2025 Apr 25;19:1133-1145. doi: 10.2147/PPA.S493933. PMID: 40302836; PMCID: PMC12039839.

Bawazir OA. Risk Factors, Diagnosis, and Management of Halitosis in Children: A Comprehensive Review. J Contemp Dent Pract. 2021 Aug 1;22(8):959-963. PMID: 34753852.

Buj-Acosta, Cindy and García-Sanz, Verónica and Bellot-Arcís, Carlos and Tortajada-Girbés, Miguel and Paredes-Gallardo, Vanessa and Tarazona-Álvarez, Beatriz and Montiel-Company, José María, Prevalence of Halitosis in Children and Associated Factors: A Systematic Review and Meta-Analysis. Available at SSRN: https://ssrn.com/abstract=4030566 or http://dx.doi.org/10.2139/ssrn.4030566

Cleveland Clinic. What is halitosis?. (2025, March 8). https://my.clevelandclinic.org/health/diseases/17771-bad-breath-halitosis

Johns Hopkins Medicine. Halitosis (bad breath). Conditions and Diseases. https://www.hopkinsmedicine.org/health/conditions-and-diseases/halitosis-bad-breath

Mayo Foundation for Medical Education and Research. (2023, December 21). Bad breath. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/bad-breath/symptoms-causes/syc-20350922

Motta LJ, Bachiega JC, Guedes CC, Laranja LT, Bussadori SK. Association between halitosis and mouth breathing in children. Clinics (Sao Paulo). 2011;66(6):939-42. doi: 10.1590/s1807-59322011000600003. PMID: 21808855; PMCID: PMC3129960.

U.S. Department of Health and Human Services. National Institutes of Health. (2023, September). Dry Mouth: Questions and Answers. National Institute of Dental and Craniofacial Research. https://www.nidcr.nih.gov/sites/default/files/202310/dry-mouth-questions-answers_0.pdf