Bad breath (halitosis) is usually caused by bacteria on the tongue and gums releasing volatile sulphur compounds. Around 85% of cases start in the mouth — gum disease, tongue coating, decay, or dry mouth. The rest trace to the sinuses, gut, diet, medication, or conditions like diabetes. Most cases are treatable once the source is found.
The reason your mouthwash never fixed it
Mouthwash and mints attack the smell, not the source. Roughly 85% of persistent bad breath originates inside the mouth; the rest traces to the sinuses, digestive system, medications, or systemic conditions. A professional hygiene appointment removes the biofilm behind most oral cases.
The mechanism
Bacteria break down food debris and protein, releasing volatile sulphur compounds (VSCs) — the smell people notice. Transient bad breath (morning breath, garlic) clears on its own; persistent bad breath has a specific cause worth identifying.
Oral causes
Tongue coating — the single commonest source; the back of the tongue traps bacteria in a biofilm most people never clean.
Gum disease — inflamed gums host large populations of odour-producing bacteria; bleeding gums are a strong clue.
Tooth decay and old dental work — cavities and failing fillings create sheltered bacterial reservoirs.
Dry mouth — saliva is the mouth's natural cleaning system; when it drops, bacteria flourish. See our guide to dry mouth causes and treatment.
Non-oral causes
Sinus and throat — post-nasal drip, sinusitis, tonsil stones. Gut and digestion — acid reflux, H. pylori, gut microbiome imbalance. Diet — garlic, onions, keto breath. Medication — many cause dry mouth as a side effect. Systemic conditions — uncontrolled diabetes, liver or kidney disease.
A self-test
Wrist test — lick your wrist, let it dry, smell it. Tongue swab — wipe the back of the tongue with a cotton swab and smell it. Floss check — smell the floss after cleaning between back teeth. Ask someone you trust.
At-home treatment that works
Clean your tongue daily with a scraper — the highest-impact change most people skip. Clean between teeth every day — brushing alone misses ~40% of each tooth's surface. Brush properly twice a day. Stay hydrated to protect saliva. Use mouthwash wisely — zinc-containing antibacterial rinses have better evidence than masking rinses. Mind your diet — reduce sugar and ultra-processed foods. More ideas are in our guide to home remedies and professional treatments.
When to see a dentist
If bad breath persists despite two to three weeks of daily tongue and interdental cleaning, or gums bleed when brushing. Hygiene appointments run 30 minutes at £85, with a deep clean included (Diamond hygiene, with air polish, is £135). See your GP instead if the mouth is confirmed healthy and you have nasal congestion, heartburn, excessive thirst, or unexplained weight change.
Bad breath and the gut microbiome
The mouth and gut share a connected microbial ecosystem. Diet shapes both at once — a whole-food diet supports more favourable populations in both. Specific oral probiotic strains have modest evidence for fresher breath.
How we approach it at DWL
Find the true source first, treat the cause not the symptom, 30-minute hygiene appointments, whole-health framing including diet and the oral-gut connection, and honest scope — referring out when the cause is outside the mouth.
Frequently asked questions
Why do I have bad breath even after brushing? Brushing misses the tongue and interdental spaces — the two biggest sources.
How do I get rid of it permanently? By treating the actual cause — tongue cleaning, interdental cleaning, gum disease treatment, hydration.
Can bad breath come from the stomach or gut? Sometimes, but only around 15% of cases are non-oral.
Are tonsil stones causing my bad breath? Possibly — small calcified deposits packed with sulphur-producing bacteria.
Does mouthwash cure bad breath? No — it masks odour temporarily; zinc rinses have reasonable evidence but don't replace cleaning.
Book a fresh-breath assessment
Hygiene appointment £85 (30 minutes). Dental examination £65 (30 minutes). Call 020 8127 4567 or WhatsApp +44 7974 910222. 222 Essex Road, Islington, London N1 3AP.
Reviewed by Dr Vishal Patel · BDS Liverpool · MSc Aesthetic & Restorative Dentistry (Manchester) · GDC 103127 · AACD Member, and Dr Reena Sohal · BDS Liverpool · GDC 104355. This article is general information, not a diagnosis. Last reviewed 2026-06-04.
