What Cause Bad Breath?

Bad breath is caused by odor-producing bacteria that grow in the mouth. When you don't brush and floss regularly, bacteria accumulate on the bits of food left in your mouth and between your teeth. The sulfur compounds released by these bacteria make your breath smell.Certain foods, especially ones like garlic and onions that contain pungent oils, can contribute to bad breath because the oils are carried to your lungs and out through your mouth. Smoking is also a major cause of bad breath.

I agree with you priyanka these are major causes for bad breath. To avoid it brush your teeth twice a day.Use a good mouth cleanser like listerine to avoid bad breath.Avoid having sugary and sticky foods late at night.

As mentioned above there are various causes of bad breadth including diabetes, Lactose intolerance, poor oral hygiene, gum disease, etc.
Gastroesophageal reflux disease (GERD) is when the muscle at the end of your esophagus does not close properly. This causes the content in stomach to leak back or reflux.You may feel burning in chest or throat and sometimes you can also feel the taste in the mouth. So this can also be one the reasons/causes for smelly breadth.