An alternative agent is chlorine dioxide, a powerful though unstable germicide that is used in water purification. Dr. Jon L. Richter, a periodontist in private practice in Philadelphia who has treated more than 5,000 patients with halitosis, said chlorine dioxide had a triple-action effect in combating bad breath: it is a deodorant, it kills odor causing bacteria and it reduces the amount of protein available for bacteria to ferment.

Chlorine dioxide is available as part of a breath-care kit produced by ProFresh that includes a tongue scraper, a brush for applying chlorine dioxide to the tongue and a test to sample the bacteria on the tongue. Other chlorine dioxide products, including Oxyfresh and Retardex, can be obtained through dentists. Products that are stabilized last longer but are less effective as a germicide.

Dr. Richard H. Price, a dentist affiliated with the Boston University Dental School, said daily tongue cleansing and the use of chlorine dioxide had enabled him to solve his own breath problem, He explained, "To be effective, you must scrape the very back of the tongue, which makes many people gag. But after a while you get used to it and you no longer gag."