Everyone feels vulnerable about oral hygiene and bad breath. Simply because one never knows till it is made embarrassingly evident by someone else. The causes may vary from tooth decay, in which a visit to the dentist is the solution, gingivitis which is decay of the gums which requires medical treatment, food particles in cavities, or plaque which requires proper brushing and flossing as also gargling. It could also be due to the tongue having a coating which requires cleaning or plain indigestion. Problems with the tonsils and nose are also possible reasons.
Given below are some links to this problem which may be of use.