Around 80% of what causes halitosis is oral issues from bacteria buildup such as cavities, gum disease, cracked fillings and poor dentures. Bacteria buildup often occurs in places a toothbrush canít reach. It then can lead to these oral issues and persistent bad breath. High-protein, low-carbohydrate diets, too many sweets, and a steady fare of onions and garlic in your diet can cause halitosis. The infections in the mouth, nose and throat something like a sinus infection, dry mouth, smoking, tobacco uses etc also cause bad breath. It may also be a sign of lung disease, certain cancers, tonsil infections, blood disorders, gastric reflux, diabetes, liver or kidney disease.