Causes of Bad Breath: From Physiological Causes to Oral and Systemic Disease
Causes of bad breath fall into physiological causes where saliva drops, pathological causes from disease, and subjective causes where worry is greater than the actual odor. The Korea Disease Control and Prevention Agency (KDCA, 질병관리청) explains that 85-90% of bad breath arises in the mouth and the remaining 10-15% from nose, throat or whole-body disease. That is why finding the cause usually starts at the dentist.
Key facts
| Oral causes | About 85-90% of bad breath (source: KDCA National Health Information Portal) |
|---|---|
| Causes outside the mouth | About 10-15% of bad breath (nose, throat, lung, whole-body disease) (source: KDCA National Health Information Portal) |
| Bacteria in the mouth | More than 300 species live there (source: KDCA National Health Information Portal) |
| Volatile compounds in breath | More than 400; their distribution and concentration determine the odor level (source: KDCA National Health Information Portal) |
| Odor compound makeup | Methyl mercaptan and hydrogen sulfide are 90% of volatile sulfur compounds (source: KDCA National Health Information Portal) |
How are the causes of bad breath broadly divided?
Physiological bad breath is odor that appears when saliva flow drops, such as just after waking, on an empty stomach or when nervous. Reduced salivary gland function with age and hormone changes during menstruation or pregnancy are also classified as physiological causes.
Pathological bad breath is odor caused by disease in the mouth or body, and subjective bad breath refers to cases where testing measures no clear odor but the person worries about it.
Either way, the odor substances are similar. Human breath contains more than 400 volatile compounds, and the important ones in bad breath are volatile sulfur compounds, of which methyl mercaptan and hydrogen sulfide account for 90%. The cause determines how much of these are produced and for how long.
What are the causes that arise inside the mouth?
More than 300 species of bacteria live in the mouth, and they make odor compounds as they break down proteins. The more places bacteria gather, the stronger the bad breath.
Among oral causes, the upper back surface of the tongue is especially important because the toothbrush rarely reaches it and many bacteria cling there. Tartar, which is hardened plaque, and gum pockets deepened by gum disease are also places where bacteria hide, so odor can occur even when the teeth look clean.
- Tongue coating built up on the upper back of the tongue
- Plaque on teeth and hardened tartar
- Cavities and food trapped around unmanaged wisdom teeth
- Gum pockets deepened by gum disease
- Old or ill-fitting dentures and prostheses
- Dry mouth from medications, Sjogren's syndrome and similar causes
What causes outside the mouth lead to bad breath?
10-15% of bad breath comes from outside the mouth. In the nose and throat, chronic rhinosinusitis, tonsil stones and secretions draining behind the nose can produce odor.
Whole-body causes include diabetes, kidney failure, liver failure, digestive tract disorders such as reflux esophagitis, and lung disease such as bronchiectasis. If these are suspected, ENT or internal medicine care takes the lead rather than the dentist.
When a cause outside the mouth is suspected, it helps to tell the doctor about symptoms that occur with the bad breath, such as nasal congestion, yellow nasal discharge, a feeling of something in the throat and heartburn. If odor stays the same after dental treatment has dealt with oral causes, it is time to look at causes outside the mouth.
How do lifestyle habits affect the causes of bad breath?
Smoking and drinking dry the mouth and worsen bad breath. Skipping meals or eating irregularly reduces saliva, and stress and fatigue also reduce saliva.
Sulfur-rich foods such as onion, garlic and scallion leave an odor for a while after eating. However, food odor fades with time, whereas bad breath from disease often lasts all day.
Mouth breathing and nasal congestion also dry the mouth. Bad breath from lifestyle often decreases when habits change, so before suspecting disease it is worth checking quitting smoking, water intake and regular meals first.
In what order are the causes of bad breath checked?
Because most causes of bad breath are in the mouth, the dentist first looks at tongue coating, tartar, cavities, gum condition and prostheses. If odor remains after treatment or no oral cause is found, an ENT clinic checks the nose and tonsils, and internal medicine checks for whole-body disease.
At the visit, history taking comes first: when the odor began, when in the day it is worse, whether the mouth is dry, smoking, drinking and eating habits, and medicines you take. This information alone can sort out much of whether the cause is physiological or a disease, so it is good to prepare it in advance.
- Step 1, dentist: check tongue coating, tartar, cavities, gum disease, prostheses
- Step 2, ENT: check for rhinosinusitis, tonsil stones, postnasal drip
- Step 3, internal medicine: check for diabetes and stomach, liver, kidney and lung disease
Common myths and facts
Myth: Bad breath is mostly caused by a bad stomach.
According to the KDCA, about 85-90% of bad breath has an oral cause. Stomach disorders are only a part of the 10-15% that come from outside the mouth.
Myth: If I brush hard, all causes of bad breath disappear.
Bacteria on the back of the tongue, between teeth and in gum pockets are not easily removed by brushing alone, so tongue cleaning, flossing and dental care are needed too.
Frequently asked questions
What is the most common cause of bad breath?
The KDCA names tongue coating on the back of the tongue, plaque, tartar and gum disease as representative oral causes. The back of the tongue is where many bacteria gather, so managing coating is important. If gums bleed when brushing, gum disease can be suspected first.
Does stress make bad breath worse?
Tension or stress reduces saliva and can cause physiological bad breath. Drinking water often and eating regularly help reduce the causes of bad breath.
Can the medicines I take cause bad breath?
Some medicines reduce saliva and dry the mouth, which can worsen bad breath. The KDCA explains that about 500 kinds of medicines reduce saliva. Do not stop medicine on your own; tell the prescribing doctor or dentist about the dry mouth.
I wear dentures; what causes bad breath?
Food and bacteria easily remain around old or ill-fitting dentures and prostheses, causing bad breath. It is good to check your denture cleaning habits and have the fit checked at the dentist.
When is a cause outside the mouth suspected?
If odor remains after the dentist has managed tongue coating, tartar and gum disease, or if nasal congestion, a feeling of something in the throat or digestive symptoms occur too, suspect a cause outside the mouth and see an ENT clinic or internal medicine.