Bad breath is an unpleasant condition that can often become a major reason for embarrassment. Causes of bad breath are:

Certain food stuffs like onion and garlic. These once absorbed in the body are transferred to lungs and expelled as bad breath.

Habitual use of tobacco and alcohol in any form.

Improper brushing of teeth which leaves behind food entangled between teeth causing bad breath.
Dry Mouth.

Gum Diseases.

Bad breath can also occur due to some underlying medical problems like diabetes, respiratory infections, kidney problems etc.