The proper amount of fluoride helps prevent and control tooth decay in children and adults. Fluoride works both while the teeth are developing and every day after the teeth have emerged through the gums. Fluoride consumed during tooth development can also result in a range of visible changes to the enamel surface of the tooth. These changes have been broadly termed dental fluorosis.

Dental fluorosis is a condition that causes changes in the appearance of tooth enamel. It may result when children regularly consume fluoride during the teeth-forming years, age 8 and younger. Most dental fluorosis in the U.S. is very mild to mild, appearing as white spots on the tooth surface that may be barely noticeable and do not affect dental function. Moderate and severe forms of dental fluorosis, which are far less common, cause more extensive enamel changes. In the rare, severe form, pits may form in the teeth. The severe form hardly ever occurs in communities where the level of fluoride in water is less than 2 milligrams per liter.

Dental fluorosis is caused by taking in too much fluoride over a long period when the teeth are forming under the gums. Only children aged 8 years and younger are at risk because this is when permanent teeth are developing; children older than 8 years, adolescents, and adults cannot develop dental fluorosis. The severity of the condition depends on the dose (how much), duration (how long), and timing (when consumed) of fluoride intake.

Increases in the occurrence of mostly mild dental fluorosis were recognized as more sources of fluoride became available to prevent tooth decay. These sources include drinking water with fluoride, fluoride toothpaste—especially if swallowed by young children—and dietary prescription supplements in tablets or drops (particularly if prescribed to children already drinking fluoridated water).