Can tooth decay cause bad breath?

Tooth decay starts when bacteria in plaque turn sugars into acid that dissolves enamel. Over time a cavity, or hole, forms. That hole becomes a sheltered pocket where food and bacteria collect beyond the reach of your toothbrush, and those bacteria break food down into smelly gases.

Decay can also hide where you cannot see it: between teeth, along the edge of an old filling, or under a crown. If decay reaches the nerve, the tooth can become infected and form an abscess, a pocket of pus. The NHS lists a bad taste in the mouth among abscess symptoms.

Early decay usually causes no symptoms, according to NIDCR, which is why regular checkups matter. As it advances, look for:

• Toothache, or sharp pain with hot, cold or sweet foods
• White, brown or black spots on a tooth, or a visible hole
• Food that always catches in the same place
• A bad smell or taste from one spot, often noticed when flossing that area
• A filling or crown that feels rough, cracked or loose

The NHS says a dental abscess needs urgent treatment by a dentist and will not go away on its own. Symptoms include intense throbbing pain, swelling inside the mouth or on the face or jaw, a bad taste, difficulty opening your mouth and chewing, swollen neck glands and a high temperature. The NHS advises calling emergency services or going to the emergency department if you have difficulty breathing, speaking or swallowing, or swelling around your eye.

A dentist can find decay with an exam and X-rays, then treat it:

• Fillings remove decayed tissue and seal the hole, removing the hiding place for bacteria.
• Replacing leaking fillings or crowns closes gaps where food was collecting.
• Root canal treatment clears infection from inside a tooth.
• Extraction may be needed if a tooth cannot be saved.

Bad breath from a cavity often improves quickly once the tooth is treated, as long as the rest of the mouth is clean too.

• Brush twice a day with fluoride toothpaste, and spit rather than rinse after brushing, as the NHS advises.
• Clean between your teeth daily, since decay often starts in the gaps.
• Cut down on how often you have sugary food and drinks. Frequent snacking gives bacteria repeated chances to make acid.
• Clean your tongue daily to reduce the overall bacterial load in your mouth and the odor it produces.
• See a dentist regularly so decay is caught before it hurts.

For a full checklist, try our oral hygiene routine builder.