Water Fluoridation Started With a Brown-Stained Town and a Curious Dentist

Frederick McKay arrived in Colorado Springs in 1901 to open a dental practice and immediately noticed something strange: many of his patients had brown, pitted enamel. The condition had been called "Colorado Brown Stain" locally for years. McKay spent the next three decades trying to understand it.

By the 1930s, working with H. Trendley Dean at the US Public Health Service, McKay confirmed that the staining came from naturally occurring fluoride in the drinking water. The pivotal observation was secondary: towns with elevated fluoride also had significantly lower rates of tooth decay, even accounting for the cosmetic damage at high doses.

Dean used data from 21 cities to plot a dose-response curve. At around 1 part per million of fluoride in drinking water, decay rates dropped substantially without the enamel mottling that appeared at higher concentrations. In 1945, Grand Rapids, Michigan became the first city to adjust its water fluoride level intentionally. By 1960, more than 50 million Americans were drinking fluoridated water.

The Grand Rapids study — 11 years of follow-up, using unfluoridated Muskegon as a control — found a 60% reduction in dental caries in children who drank fluoridated water from birth. The CDC named water fluoridation one of the ten great public health achievements of the 20th century in 1999.

The debate has never fully closed. Concerns about thyroid function and IQ effects at higher doses have produced court challenges and municipal opt-outs. The evidence for harm at 0.7 ppm — the current US standard — remains weak. The evidence for caries reduction remains strong.