12 Bad Breath Causes from Sneaky Medical Problems, According to a Doctor

Updated: Oct. 26, 2023

You know it's time to freshen up when your breath is getting on your own nerves. A dentist reveals under-the-radar causes of bad breath.

Bad Breath Mouth
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You brush every morning and night, floss once a day, and chew a stick of mint gum every now and then and even use a water flosser—so why does your breath still bug you (or draw comments from someone who loves you)? If you’re having persistent issues with bad breath, there may be an underlying health issue behind the problem.

As a dentist and author of If Your Mouth Could Talk: An In-Depth Guide to Oral Health and Its Impact on Your Entire LifeI shared with The Healthy @Reader’s Digest what causes bad breath and what you can do about it.

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What causes bad breath?

1. Acid reflux

Acid reflux (also called GERD when it becomes chronic), is caused by stomach acid flowing back up the esophagus, which can also bring undigested food with it…accompanied by a sour odor.

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2. Bronchitis

When your bronchial tubes get infected, they swell and you end up with a terrible cough, congestion, and bad-smelling mucus and breath.

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3. Dehydration

If you’re dehydrated, your body may not produce enough saliva, which causes dry mouth and an excess of bacteria in your mouth.

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4. Diabetes

This lack of insulin causes your body to burn fat rather than sugar, which produces ketones, like acetone, in your body. If your breath smells fruity or like nail polish, it may be diabetes.

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5. Diet

What causes bad breath? It could be what you’re eating. A diet high in onions and garlic is delivering some fierce antioxidants, but also likely some potent breath. With good oral health, that’s usually nothing to worry about.

Low carb diets, however, can cause the release of ketones like acetone, just like diabetes.

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6. Infections

Any infection of the nose, sinus, throat, or tonsils can cause bad breath.

Can Allergies Cause a Sore Throat? Here’s What Doctors Say

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7. Kidney problems

If your kidneys aren’t functioning correctly, they’re unable to filter minerals out of your blood properly, causing them to build up in your body. This can make your breath smell of ammonia, or even call to mind the scent of urine.

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8. Liver problems

When your liver isn’t working correctly, it can’t regulate your blood sugar or filter toxins from your blood. This can cause bad breath with a musty, sweet smell.

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9. Medications

Some medications give you dry mouth, while others release chemicals in your body that can cause bad breath.

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10. Pneumonia

This infection can be viral or bacterial, but the buildup of fluid in your lungs can smell foul—and if you cough it up, the smell will carry on your breath.

7 Signs Your Upper Respiratory Infection Is Actually Pneumonia

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11. Post-nasal drip

If mucus builds up in the back of your throat, it can travel to your mouth or build up around your tonsils, causing bad breath.

9 Things Your Bad Breath Reveals About Your Health

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12. Tobacco use

Using tobacco products causes a buildup of odor-causing agents in your mouth, airways, and lungs, and also causes dry mouth. It can also cause oral diseases, which can cause bad breath as well.

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About the Expert:

Dr. Kami Hoss, DDS, MS, is a San Diego-based orthodontist and dentofacial orthopedist, author, and founder of The Super Dentists and Howard Healthcare Academy. He is on the Board of Counselors at UCLA School of Dentistry where he previously received his doctorate in dental surgery. Dr. Hoss is a nationally recognized speaker and a sought-after expert focusing on oral health and its impact on overall health and emotional well-being.