What usually causes persistent bad breath?
Most persistent oral malodor is associated with bacterial metabolism on the tongue, teeth and gum areas, although dry mouth, tobacco, diet, periodontal disease and non-oral causes can also contribute.
Volatile sulfur compounds are commonly used as measurable markers in halitosis research. Because several causes can produce the same symptom, a useful strategy starts with cleaning the tongue and interdental areas, improving hydration, treating dental disease and checking for dry mouth or other triggers.
If odor remains despite good hygiene, dental assessment is more useful than repeatedly masking the smell.
What does microbiome research suggest?
Microbiome studies suggest that changing the abundance or activity of odor-associated organisms may influence breath-related outcomes, but effects depend strongly on the intervention used.
A randomized trial of live and heat-killed Lactobacillus paracasei ET-22 reported reductions in breath volatile sulfur compounds and changes in salivary microbial composition after four weeks. A 2025 systematic review of probiotic trials also found that several studies reported reductions in VSCs or organoleptic scores, while noting substantial heterogeneity and limited long-term evidence.
These findings support the biological plausibility of microbiome-targeted approaches. They do not establish that every probiotic or postbiotic product will improve halitosis.
Why tongue cleaning and saliva still matter more
A supplement cannot compensate for a heavily coated tongue, plaque accumulation or chronically dry mouth.
The tongue has a large surface area that can retain debris and odor-producing bacteria. Saliva helps clear food particles and buffers the oral environment. Hydration, managing dry-mouth triggers and cleaning the tongue gently can therefore address major drivers directly.
For people with gum disease, odor may persist until the underlying inflammation and periodontal pockets are treated.