There are many reasons of halitosis or bad smell from the mouth like accumulation of food deposits,,decayed teeth or gastric problem..First of all start brushing twice daily after meals,use a mouthwash,get scaling done from a dentist and the cavities filled up if any.If still the bad smell doesnot subside,,then see a gastroenterologist.

Hello There are different reasons for bad breath. Calculus / stains / gingivitis are dental reasons. You can get your teeth cleaned by dentist to solve this . Chronic gastritis could be other one . Hormonal changes may be another one . After fasting gastric problem , too much of coffee and beverages could be some of reasons . The treatment goes accordingly . Thanks