One of the most common elements on Earth, fluoride is naturally present in human bodies and water, and common in toothpaste and mouthwash. And for decades, the mineral has been added to the water supplies of thousands of communities across the United States to help prevent dental cavities and decay.

Florida’s Surgeon General is the latest high-profile politician to advise against adding fluoride to drinking water. For decades it’s been credited with keeping teeth healthy, but now some are starting to question if it is necessary or even harmful in high doses.