People concerned about their bad breath often take recourse in a “good” mouthwash, meaning one that has a high alcohol concentration and leaves the mouth smelling minty or like cinnamon. The problem with many products marketed as bacteria-killers and breath-fresheners is that they can easily dry out your mouth.
Bad breath commonly comes from food particles, poor dental hygiene or dry mouth. The latter contributes to halitosis by allowing odor-causing bacteria to grow. They live on food particles and oils on the tongue and teeth, which they digest and use to create odor molecules. The most common molecule in bad breath is hydrogen sulfide, which makes every lungful of breath you exhale smell like rotten eggs.
It is easy to think that typical mouthwash will eliminate the problem, since alcohol kills bacteria. It does not kill all oral bacteria, however. Often you will see that a particular brand eliminates 99.99% of the microorganisms in your mouth. That leaves one in every 10,000 alive and well and ready to re-multiply.
The environment those leftover bacteria are left in is a mouth dried out by alcohol, a perfect environment for bacterial growth.
Those with persistent bad breath may consider switching from mouthwash to specialty breath freshening products that moisten the palate and neutralize odor.