Bad breath
What Causes Bad Breath? Where Most Cases Actually Start
Published 2026-10-31 · Educational guide
What halitosis is
Halitosis is an unpleasant odor from the breath. Odor is caused mainly by anaerobic bacteria that break down proteins and release volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan.
The main oral causes
A systematic review published in 2023 found that intra-oral factors cause 80 to 90 percent of halitosis, with coated tongue, periodontal disease, and poor oral hygiene as the main drivers.
The tongue is a common hiding place. Its uneven surface traps bacteria that produce odor, which is why tongue care matters.
- Coated tongue (the most common single factor)
- Gum disease (gingivitis and periodontitis)
- Tooth decay and food trapped between teeth
- Dry mouth, when saliva flow drops
- Dentures that are not cleaned
Less common causes
Some non-oral conditions can cause bad breath, including sinus infections, postnasal drip, chronic bronchitis, diabetes, digestive problems, and liver or kidney disease. These are usually considered only after oral causes have been checked.
When to see a professional
If bad breath continues despite brushing, flossing, and tongue care, a dentist can check for oral causes. If the dentist finds none, a physician can look for other causes.
Frequently asked questions
Is bad breath usually caused by the stomach?
Usually not. In healthy people, most cases start in the mouth. Stomach-origin odor is rare and is linked to specific conditions.
Can brushing alone fix bad breath?
Brushing helps, but it often doesn’t reach the tongue’s back surface or the spaces between teeth. Tongue cleaning and interdental cleaning are usually needed too.
Sources
Guides from The Change Forge
Practical, source-based guides on everyday habits. Each one explains what the evidence supports, with steps you can try one at a time.
Fresh Breath Protocol
Aliento Neutro