Bad Breath: Causes, Home Care and When to See a Dentist

Bad breath is caused by volatile sulfur compounds that oral bacteria produce when they break down protein. The Korea Disease Control and Prevention Agency (KDCA, 질병관리청) says 85-90% of pathological bad breath originates in the mouth. So if odor persists despite brushing, tongue cleaning and flossing, the usual first step is a dental check of tongue coating, tartar and gum condition. In Korea, people aged 19 and over can get scaling once a year under National Health Insurance.

Published 2026-11-08 · Updated 2026-11-08 · DentalStatics editorial team

Key facts

Share from the mouth	85-90% of pathological bad breath comes from problems inside the mouth (source: KDCA National Health Information Portal)
How common	About 50% of middle-aged and older people have bad breath (source: KDCA National Health Information Portal)
Main odor compounds	Methyl mercaptan and hydrogen sulfide make up 90% of volatile sulfur compounds (source: KDCA National Health Information Portal)
Device reading standard	Halimeter 75 ppb or more is bad odor; 120 ppb or more is very severe odor (source: KDCA National Health Information Portal)
Tongue cleaning advice	Twice a day, gently 3-4 strokes from back to front of the tongue (source: KDCA National Health Information Portal)
Water intake	About 1.5 liters a day (source: KDCA National Health Information Portal)
Complaint vs. measurement	A report found about 30% of people complaining of bad breath had no objective evidence of it (source: KDCA National Health Information Portal)
Scaling under insurance	Once a year for ages 19 and over (January 1 to December 31) (source: National Health Insurance Service (NHIS))

Why does bad breath happen?

The main cause of bad breath is volatile sulfur compounds that oral bacteria make when they break down proteins and amino acids from food debris and shed cells. The KDCA explains that methyl mercaptan and hydrogen sulfide account for 90% of these compounds.

Bad breath is divided into physiological, pathological and subjective types. Odor that appears briefly when saliva drops, such as right after waking or on an empty stomach, is physiological. When testing finds no clear odor but the person keeps worrying about it, it is classified as subjective.

Human breath contains more than 400 volatile compounds, and their types and concentrations determine how strong the odor is. It is common enough that about 50% of people have bad breath in middle or old age, so checking the causes step by step is more useful than feeling embarrassed.

How are causes inside and outside the mouth divided?

Most pathological bad breath starts in the mouth. Common causes are tongue coating at the back of the tongue, plaque and tartar between teeth and gums, cavities, gum disease, and old or poorly fitting prostheses.

Causes outside the mouth include chronic rhinosinusitis, tonsil stones, stomach and intestinal disorders, lung and bronchial disease, liver and kidney disease, diabetes and Sjogren's syndrome. In such cases, ENT or internal medicine care may also be needed.

Low saliva is another important cause. Saliva washes away and suppresses bacteria, but with aging, long-term medication or mouth breathing, saliva decreases and odor compounds spread more easily.

Mouth causes: tongue coating, tartar, cavities, gum disease, dry mouth, ill-fitting dentures or prostheses
Nose and throat causes: chronic rhinosinusitis, tonsil stones, postnasal drip
Whole-body causes: diabetes, stomach disorders such as reflux esophagitis, liver and kidney disease

How can I check my own bad breath?

People often cannot smell their own breath. The KDCA introduces methods such as breathing into a paper cup and smelling it, licking the back of the hand and smelling it after it dries, smelling used dental floss, and asking family, while noting that self-assessment can be inaccurate.

Dental clinics and hospitals measure total volatile sulfur compounds with a Halimeter and concentrations by component with an Oral Chroma. A sensory test, in which a trained examiner smells the breath and scores it from 0 to 4, is also used.

A Halimeter reading of 75 ppb or more is generally regarded as bad breath, and 120 ppb or more as very severe odor. If a cause outside the mouth seems likely, tests such as a saliva flow rate test, blood tests and nose and throat endoscopy may be added.

What home care reduces bad breath?

The basics are brushing, tongue cleaning and flossing. A tongue cleaner is recommended twice a day, gently 3-4 strokes from back to front, and rubbing too hard or too often can inflame the tongue.

Drinking water often to keep the mouth from drying and using sugar-free gum to stimulate saliva also help. Foods high in sulfur such as onion, garlic and scallion, alcohol and smoking, and sugary snacks can worsen bad breath.

The KDCA recommends about 1.5 liters of water a day. When bad breath is severe, a diet with less protein-rich food such as dairy (cheese, milk) and meat and more vegetables and fruit may also help.

Brush starting at the gumline and use dental floss
Gently remove coating from the back of the tongue
Drink water often; use a humidifier while sleeping
Quit smoking, drink less alcohol, eat regular meals

Does mouthwash alone solve bad breath?

The KDCA explains that commercial mouthwash only reduces bad breath for a short time and has no lasting therapeutic effect. Misusing products that contain ethanol or antibacterial ingredients can dry the mouth and make bad breath worse.

The Ministry of Food and Drug Safety (MFDS, 식품의약품안전처) advises adults and children aged 6 and over to use 10-15 mL once or twice a day, holding it in the mouth for about 30 seconds and then spitting it out. Directions differ by product, so check the label first.

People whose mouths often feel dry are better off with an alcohol-free product, since alcohol-based mouthwash can dry the mouth further. Mouthwash cannot replace brushing and tongue cleaning, so think of it only as a supplement to bad breath care.

How does a dentist treat bad breath, and what does it cost?

At the dentist, finding the cause comes first. If tartar and gum disease are the cause, gum treatment such as scaling or root planing is done; if cavities or ill-fitting prostheses are the cause, those are treated. A medicated mouth rinse or artificial saliva may be prescribed when needed.

When tongue coating is very thick and does not come off with a tongue cleaner, a dentist may remove it with an ultrasonic scaler. If chronic rhinosinusitis or tonsil stones are confirmed as the cause, treatment is given by an ENT clinic.

For ages 19 and over, when treatment ends with tartar removal alone, scaling is covered by National Health Insurance once a year (January 1 to December 31), and beyond that it is not covered. Costs of other bad breath treatments vary by cause and clinic, so check before the visit.

When should I see a doctor for bad breath?

If odor continues despite steady brushing, tongue cleaning and flossing, it is advisable to have a dentist check the cause. If no oral cause is found, follow-up goes to an ENT clinic or internal medicine.

When you go, tell them when the odor began, whether it is worse only in the morning or lasts all day, and what medicines you take and your smoking and drinking habits; this helps narrow the cause. If any of the symptoms below also occur, it is better to book a visit without delay.

Gums bleed or swell, or teeth feel loose
The mouth is often dry and swallowing is uncomfortable
Yellow granules come up from the throat or the nose is often blocked
Family or others repeatedly point out your bad breath

Detailed guides

Frequently asked questions

Is bad breath most often caused by a bad stomach?

No. The KDCA explains that 85-90% of pathological bad breath comes from the mouth. Stomach disorders can also be a cause, but checking tongue coating, tartar and gum disease first is the usual order.

Why do I still have bad breath after brushing?

Bacteria on the back of the tongue, between teeth and inside gum pockets are not easily removed by brushing alone. Add tongue cleaning and flossing, and if odor remains, have a dentist check for tartar or gum disease. If you also have a dry mouth, less saliva may have let bacteria increase.

Is there anything to watch out for before a bad breath test?

The KDCA advises no brushing, smoking or chewing gum for 2 hours before a bad breath test. Preparing the medicines you take and when the odor started helps the search for a cause.

Does scaling reduce bad breath?

If tartar and plaque are the cause, bad breath may decrease after scaling. For ages 19 and over it is covered by National Health Insurance once a year, and if gum disease is deep, gum treatment beyond scaling may be needed. You can check whether you have already used this year's insured scaling at the dental clinic or in the National Health Insurance Service (NHIS, 국민건강보험공단) app.

What if no one smells anything but I keep worrying?

A report found that about 30% of people complaining of bad breath had no objective evidence of it. You can measure with a device to see the numbers, and if anxiety is strong, repeat measurements and counseling can help.

Do children's bad breath have the same causes?

Children can also have bad breath from cavities, tongue coating or mouth breathing, and sometimes from nasal congestion or tonsil problems. If it continues after checking brushing habits, have it checked by a dentist or pediatrician.

References

Korean version →