Bad breath (halitosis) can have many causes. Removing bacteria from your mouth is an easy way to start to eliminate bad breath. Brushing, flossing and having professional dental cleanings may be all that is needed. Infections of the mouth, such as abscessed teeth or periodontitis (gum disease), are common causes of bad breath. Untreated cavities may also be linked with halitosis. A complete dental examination can help rule these things out. Other factors that may play a role include dry mouth, sinus infections, post-nasal drip, tonsil stones, tonisillitis, acid reflux and diet.