Fluoride has its maximum effect in preventing tooth decay when it actually comes in contact with tooth enamel, so it makes sense to put fluoride in mouthwash and toothpastes, which are applied directly to the teeth. The effect on breath is rather indirect: bacteria present in dental plaque produce acids while they are breaking down ingested sugar, and this acid, in turn wears down the tooth enamel by demineralizing it (dissolving out the calcium and phosphate minerals that make enamel so tough). Saliva then neutralizes the acid and the minerals are reabsorbed. When fluoride is present, remineralization is more efficient and is believed to produce a stronger enamel. When remineralization does not replace all of the lost minerals, cavities appear. Some of the acid producing bacteria also produce volatile sulfur compounds, which cause the offensive odor of bad breath - they proliferate when the teeth and gums are unhealthy, so the idea is to prevent tooth decay with flouride and bad breath will be avoided as well.

Unfortunately, its not that easy. For one thing, fluoride is a toxin at high levels, so putting fluoride in mouthwash adds to an already high intake in people who drink fluoridated water and brush with fluoride containing toothpaste. The major risk comes when you swallow the products, so take care to spit out mouthwash and rinse to minimize ingestion. Swallowing too much fluoride, once thought to be harmless, is now associated with a number of health problems including weak bones, a form a bone cancer, damage to the teeth, and several other conditions. The link between fluoride and bad breath is tenuous at best - if your teeth are healthy, there's no reason to use more fluoride. Look for a mouth wash that doesn't contain it.

Remember that most of the bacteria that produce volatile sulfur compounds live on the tongue, down in the tiny crevices between the taste buds, protected from saliva and oxygen by a layer of mucus. Others live in creases in the gums and cheeks, in pockets around the teeth and between the teeth. When it comes to these bacteria, there is no point at all in putting fluoride in mouthwash - the ingredient neither harms nor helps them. The best approach is to try to lower their numbers by other means, such as inhibiting their growth or removing them from the mouth. Given the minimal benefit and the possibility of harm, fluoride and bad breath is not a relationship anyone should be focusing on.

R. Drysdale is a freelance writer with more than 25 years experience as a health care professional. She is a contributing editor to Fluoride and Bad Breath at Bad Breath Cure, a blog dedicated to the treatment of bad breath.