Why does post nasal drip cause bad breath?

Glands in your nose and throat make mucus all day; Cleveland Clinic puts it at one to two quarts a day. Normally you swallow it without noticing. Postnasal drip is when there is more mucus than usual, or it is thicker, so you feel it gathering in your throat or dripping down from behind your nose.

Typical symptoms include a constant urge to clear your throat, a cough that is worse at night, a sore or scratchy throat, hoarseness and, for many people, bad breath.

Most bad breath comes from bacteria on the back of the tongue, which break down proteins and release sulfur gases. The back of the tongue is exactly where postnasal mucus lands. Mucus is rich in proteins, so a steady drip is thought to give those bacteria extra material to work on, and the coating at the back of the tongue tends to get thicker.

If the drip comes from an infection such as sinusitis, the mucus itself may also smell, and you may notice a bad taste. Mouth breathing from a blocked nose dries the mouth out, which makes things worse because saliva normally rinses bacteria away.

• Allergies. Cleveland Clinic calls allergies one of the most frequent causes. See allergies and bad breath.
• Colds and flu. Usually short-lived.
• Sinus infections. Often with thick yellow or green mucus and facial pain. See sinus infection bad breath.
• A deviated septum, which can stop mucus draining properly.
• Cold or dry air and changes in weather.
• Certain medicines, including some birth control and blood pressure medicines.
• Pregnancy and acid reflux (GERD).

Tackle the drip and the tongue at the same time:

1. Rinse your nose with salt water. The NHS describes a simple homemade saline rinse for catarrh and sinusitis, and pharmacies sell ready-made kits. Use boiled and cooled or sterile water.
2. Drink plenty of fluids so mucus stays thinner and your mouth stays moist.
3. Clean the back of your tongue every day. This is where drip mucus and bacteria build up. Reach as far back as you comfortably can without gagging, using light strokes from back to front.
4. Gargle with warm salt water to loosen mucus in the throat.
5. Treat the trigger. A pharmacist can advise on antihistamines or steroid nasal sprays for allergies. The NHS says decongestant sprays should not be used for longer than 5 days.
6. Use a humidifier if dry indoor air makes it worse.

Mints and mouthwash may cover the smell for a short time, but they do not remove the mucus coating, so the smell comes back.

Our bad breath test can help you narrow it down.

Cleaning the back of the tongue makes sense here because that is where drip mucus and odor bacteria collect, and a review in the Journal of Breath Research identifies tongue coating as one of the two main sources of odor gases in the mouth. The controlled trial evidence is modest, though: a 2019 Cochrane review of treatments for bad breath found only two small tongue-cleaning trials, with 46 people in total, and rated the evidence as very low certainty. It is a cheap, low-risk habit worth trying, not a guaranteed cure, and it works best alongside treating the drip itself.

The NHS advises seeing a GP if catarrh lasts more than a few weeks or you get new symptoms such as a sore throat, problems swallowing or loss of smell, so they can rule out things like nasal polyps. MedlinePlus advises contacting a provider if bad breath comes with signs of a respiratory infection such as fever, cough or facial pain with nasal discharge.