Bad breath, also known as halitosis, is breath that has an unpleasant odour.

Bad breath can be caused by:

• Poor dental hygiene — Infrequent or improper brushing and flossing can leave food particles to decay inside the mouth
• Infections in the mouth — Periodontal (gum) disease
• Respiratory tract infections — Throat infections, sinus infections, lung infections
• External agents — Garlic, onions, coffee, cigarette smoking, chewing tobacco
• Dry mouth (xerostomia) —This can be caused by salivary gland problems or by medications 
• Systemic illnesses — Diabetes, liver disease, kidney disease, lung disease, sinus disease, reflux disease and others
• Psychiatric illness — Some people may perceive that they have bad breath, but it is not noticed by oral-health-care professionals or others. This is referred to as "pseudohalitosis."