Bad smell is associated with multiple reasons like decayed tooth, harnessing of food particles in the decayed tooth, calculus(yellow deposits around teeth), swelling of gums, etc.
Get it evaluated clinically by visiting your nearby dentist and follow the treatment plan advised by the doctor. Also, do following lifestyle modifications:
1. Drinking sufficient water throughout the day
2. Eating plenty of salads and fresh fruits
3. Gargle after every meal
Next Steps
Visit nearby dentist and do lifestyle modifications