Mouth Breathing and Bad Breath: Why Your Breath Smells Even After Brushing

Short answer: Brushing twice and still bad breath? Mouth breathing dries the mouth so odour-causing bacteria grow, and swallowed air worsens reflux.

Medically reviewed by Dr. Prashanth R. Reddy, ENT Surgeon (MS ENT) · Last reviewed: 31 October 2026

How mouth breathing causes bad breath

Saliva constantly washes the mouth and keeps odour-causing bacteria in check. Breathing through the mouth, especially at night, dries it out. In a sleep study, mouth breathing made the mouth markedly drier and more acidic overnight (Choi et al., 2016). Odour-causing bacteria thrive in that dry, acidic environment, mostly on the back of the tongue.

Mouth breathers also swallow more air. That bloats the stomach and pushes acid up into the throat, and silent reflux (LPRD) adds its own sour smell. Read Bad breath that won't go away? The silent reflux link.

Why mouthwash doesn't solve it

A rinse masks the smell for an hour or two. It doesn't bring back saliva or stop the drying, so the smell returns.

Why do people breathe through the mouth?

Usually because the nose doesn't let enough air through. Common reasons are a deviated septum, swollen turbinates, nasal allergy, chronic sinusitis, nasal polyps and, in children, enlarged adenoids and tonsils. Sometimes it starts as a habit and stays even after the nose clears.

Signs you or your child may be a mouth breather

• Lips apart at rest or during sleep
• Snoring, dry mouth or drooling on the pillow
• Waking tired, dark circles under the eyes
• Bad breath and frequent throat clearing
• Always 'blocked' nose, especially at night

What helps

1. Find out why the nose is blocked. An ENT evaluation (examination plus a CT scan of the nose where needed) shows whether it's the septum, turbinates, allergy, sinuses or adenoids.
2. Treat the cause, from allergy control and nasal sprays to correcting a blockage when it's needed.
3. Work with your dentist or orthodontist on the teeth, gums and bite.
4. Re-train nasal breathing once the nose is open, with lips closed at rest.

When to see an ENT

If you or your child breathe through the mouth most of the time, snore, or have a constantly blocked nose, an ENT evaluation can find the cause.

References

• Choi JE, et al. Intraoral pH and temperature during sleep with and without mouth breathing. Journal of Oral Rehabilitation. 2016;43(5):356-363.

Related reading: Mouth breathing and tooth decay · Mouth breathing and gum disease · Mouth breathing and crooked teeth · Mouth breathing and a high-arched palate · Mouth breathing, a receding jaw and a long face

About the author

Dr. Prashanth R. Reddy is a Senior Consultant ENT Surgeon in Bengaluru (MS ENT; Fellowship in Rhinoplasty, Seoul; MBA, IIM Bangalore) with over two decades of practice. He sees patients at Sakra World Hospital, Marathahalli and at the ENTHealth360 clinic in Koramangala.

For educational purposes only. Not a substitute for medical advice. Please consult a qualified ENT specialist.