Persistent foul smell from the mouth is most commonly caused by poor oral hygiene, plaque and tartar buildup, gum infection, tooth decay, food particles trapped between the teeth, dry mouth, or poor tongue cleaning. Smoking, tobacco use, throat infections, sinus problems, tonsil stones, acid reflux, diabetes, and some stomach conditions can also contribute to bad breath. The best treatment depends on finding and treating the underlying cause. Maintaining good oral hygiene is very important, including brushing twice daily with a soft toothbrush, cleaning the tongue regularly, flossing between the teeth, and rinsing the mouth after meals. Drinking enough water can help prevent dryness in the mouth, which often worsens bad breath. An antibacterial mouthwash may provide temporary relief, but if tartar or gum disease is present, professional dental cleaning (scaling) is usually needed for effective and long-lasting improvement. Avoid smoking, tobacco, and excessive sugary foods because they can worsen mouth odour and gum disease. Eating fresh fruits and vegetables and maintaining a healthy diet may also help improve oral health. If you have gum bleeding, loose teeth, mouth ulcers, tooth pain, white patches, fever, or bad breath that continues despite good oral care, you should consult a dentist or doctor for proper examination and treatment. Early treatment of the root cause usually gives the best relief and helps keep the mouth healthy.