There are many things that can cause bad breath. If you breathe thru your mouth instead of your nose (due to polyps, cold etc), bacterias (MRSA & PA have distinct ordors), not brushing, flossing & gargling (be sure to do the tongue as well as your teeth) which allows food, meds & buildup from nebs to accumulate as well as acid reflux (even if you dont "feel" it).
Dehydration will do it also.
Dehydration will do it also.