Poor oral hygiene
The most common cause of bad breath is poor oral hygiene. Bacteria that build up on your teeth particularly between them as well as your tongue and gums, can produce unpleasant smelling gases. These bacteria are also responsible for gum disease and tooth decay.
Food and drink
Eating strongly flavoured foods such as garlic, onions and spices are likely to make your breath smell. Strong-smelling drinks, such as coffee and alcohol, can also cause bad breath. Bad breath caused by food and drink is usually temporary. It can be avoided by not eating or drinking these types of food and drink too often.
Smoking is another cause of bad breath. As well as making your breath smell, smoking stains your teeth, irritates your gums, and reduces your sense of taste. It can also significantly affect the development of gum disease, another major cause of bad breath. Stopping smoking will lower your risk of gum disease and help prevent bad breath.
Crash dieting, fasting, and low-carbohydrate diets are another possible cause of bad breath. They cause the body to break down fat, which produces chemicals called ketones that can be smelled on your breath.