Bad breath is an unpleasant odor from the mouth or nose medically known as halitosis; in most cases, it originates from the mouth itself. Oral malodor (bad breath) can be long or short term depending on the cause, and some are due to gum disease, mouth infection, sinus infections, gastric reflux, cavities, and renal failure or diabetes complications. Most commonly the major cause of bad breath is poor dental hygiene which is due to the release of sulfur compounds by bacteria in the mouth. Other factors may include not brushing the teeth regularly, not flossing, dry mouth, tobacco intake and poor diet which can lead to accumulation of debris, plaque build-up in the teeth and bacteria in the mouth. 
You might not know if you have bad breath because the cell responsible for odor detection in your nose is used to the smell; the only way is the people react when you talk. So either having it or not there are remedies we have provided to prevent and treat bad breath no matter the cause.