Bad breath after you get up in the morning is a common phenomenon. But if it bothers you all day long there is a reason to worry as there are some factors that contribute to giving you a foul smell. Eating fast foods is one of the surprising causes of bad breath. But the cause is not the onions in the burger. The cause is the greasy residue in burger and fries that lead to a smelly chain of reaction in your body causing bad breath. The oils in the fries interact with your digestive enzymes and cause dragon breath.