“It prevents tooth decay!”

“It causes cancer!”

Rarely has any chemical substance been as polarizing as fluoride. So what's the deal?

First of all, what is fluoride? It's a negative ion of the element fluorine and occurs in trace amounts all around you – rocks, air, soil, plants, fresh and sea water – you name it. It plays a big role in the mineralization of your bones and teeth, the process that keeps them strong. Ninety-nine percent of the fluoride in your body can be fond in your bones and teeth.

Fluoride was first added to a public water supply in 1945, when Grand Rapids, Michigan, became the first city to “fluoridate” its drinking water. The dental cavities rate among Grand Rapids children dropped 60 percent, and a public health phenomenon was born.

Tooth decay – sometimes referred to as “dental caries – is caused by bacteria living in your mouth, and is one of the most prevalent chronic diseases affecting people worldwide. Despite this, fluoridation is rare in Europe. Many of those opposed to it believe dental hygiene should be handled on an individual level and not through “mass medication.”

These bacteria break down carbohydrates and generate organic acids that can damage tooth enamel (that's why your dentist has been warning you away from eating “too many sweets” for as long as you can remember). The acid “de-mineralizes” your teeth, and the fluoride “re-mineralizes” them; when the effects of the acid out-pace the affects of fluoride's patch-up, tooth decay occurs.  Fluoride is also able to reduce acid production by interfering with the activity of bacterial enzymes.

In the 80s, scientists discovered that the best way to introduce fluoride into your mouth's eco-system was to apply it directly to your teeth, and so toothpaste brands began including it along with whatever makes mouths “feel fresh and minty.”

But fluoride's reputation is not all spearmint rainbows. Too much of it can cause dental fluorosis, a teeth-altering condition causing a cosmetic defect.

Skeletal fluorosis is a bone disease borne of the accumulation of fluoride in your bones over many years. We don't really see much of it in America because the public water supply is so tightly regulated, but in places like India and China, it has caused health crises.

But the more alarming tales of fluoride contamination have it causing cancer, and bone cancer (osteosarcoma) in particular. The good news is that multiple studies have concluded there is no clear link between fluoride and bone cancer, or even just cancer in general.

The bottom line? Continue to brush with toothpastes containing fluoride, and be thankful – for your teeth's sake at least – that you live in the U.S.