Diet and poor oral hygiene are the most common causes of bad breath. It may be simply corrected by using your toothbrush to brush your tongue. Food, coffee and bacteria collect on your tongue and create a coating which causes odor. Bacteria produce sulfides which may require more extensive measures to combat the problem. Gum disease is another common cause of mouth odor. This should be evaluated by the hygienist and dentist to help determine the origin of the problem.