Chronic bad breath — clinically known as halitosis — affects an estimated 25% of adults globally, making it one of the most common oral health complaints. Yet despite its prevalence, it remains widely misunderstood. Many people who experience it brush more vigorously or use stronger mouthwashes, only to find the problem persists.
The reason, in most cases, is that chronic halitosis is not primarily a hygiene problem. It is a microbial problem.
Where Bad Breath Actually Comes From
The unpleasant odour associated with bad breath is primarily caused by volatile sulphur compounds (VSCs) — gases produced by anaerobic bacteria as they metabolise proteins and amino acids. The main culprits are hydrogen sulphide (which smells like rotten eggs) and methyl mercaptan (which smells like decaying cabbage).
These bacteria don't thrive in the visible, well-oxygenated areas of the mouth. They prefer the back of the tongue, the gum pockets, and the spaces between teeth — areas that are poorly reached by standard brushing and where oxygen levels are low.
The quantity of VSCs produced depends on the balance of bacterial species present. When harmful, protein-metabolising anaerobes dominate the oral microbiome, VSC production increases. When the balance shifts toward more benign bacterial species, it decreases.
Key point: Research has found that people with chronic halitosis consistently show elevated levels of specific bacterial species in their oral microbiome — not simply more bacteria overall, but a different composition of bacteria.
The Mouthwash Problem
Many commercial mouthwashes use alcohol as an active ingredient. Alcohol is a temporary antibacterial agent — it kills bacteria on contact. The problem is that it is non-selective: it kills beneficial bacteria alongside harmful ones, and it significantly reduces saliva production through its drying effect.
Saliva is one of the primary natural defences against the bacterial overgrowth that causes bad breath. When mouthwash use chronically reduces salivary flow, it can paradoxically worsen the conditions that lead to halitosis over time, while providing short-term improvement through temporary bacterial suppression.
Non-Oral Sources of Bad Breath
While the majority of chronic bad breath originates in the oral cavity, it's worth noting that some cases have systemic causes:
- Gastroesophageal reflux (GERD) — stomach acid and gases can contribute to breath odour
- Sinus infections or post-nasal drip — mucus draining into the throat can be metabolised by oral bacteria
- Kidney or liver dysfunction — in severe cases, can produce characteristic breath odours (ammonia-like or musty, respectively)
- Certain dietary patterns — high-protein or ketogenic diets can produce ketone-related breath odour
If bad breath persists despite good oral hygiene, it's worth discussing with a healthcare provider to rule out systemic causes.
What Actually Helps
Strategies with the strongest evidence base for addressing chronic halitosis include tongue cleaning, consistent flossing to reduce interdental bacterial accumulation, adequate hydration to support saliva production, and approaches aimed at supporting a healthier oral bacterial balance rather than simply suppressing bacteria temporarily.
Zinc-containing oral care products have reasonably good evidence behind them — zinc binds to VSCs and inhibits their production, and also has demonstrated antibacterial effects against the specific species most associated with halitosis.