Municipalities across the U.S. have been safely adding fluoride to their tap water for decades, and reams of data prove the mineral has worked wonders in strengthening enamel and preventing tooth decay. But communities could soon start removing or lowering levels of fluoride in public drinking water as misinformation about its purported harms gains dangerous momentum among media outlets and a growing number of prominent political figures.
Thank you for reading this post, don't forget to subscribe!This month Robert F. Kennedy, Jr.—President-elect Donald Trump’s current nominee for the next secretary of the U.S. Department of Health and Human Services (HHS)—fueled a fluoride furor on social media when he called the mineral “industrial waste.” Kennedy, a former presidential candidate, inaccurately claimed fluoride exposure could lead to arthritis, bone cancer, thyroid disease, IQ loss and neurodevelopmental conditions. He has said he would advise against adding it to tap water—a practice that currently reaches more than 209 million Americans.
It remains unclear whether the incoming Trump administration could effectively ban water fluoridation: current laws let state and local governments make the decision. But at the federal level, fluoridation opponents could deploy the Safe Drinking Water Act, which regulates water contaminants nationally. They could also take advantage of a recent federal court decision: In September a California district court judge ordered the Environmental Protection Agency to set stricter regulations on tap water fluoride levels, arguing that the HHS’s national concentration recommendations might lower children’s IQ scores. But the judge leaned heavily on a recent controversial scientific report that had been rejected twice in peer review for a lack of rigor.
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“His conclusion was misguided—and an overreach,” says Charlotte W. Lewis, a pediatrician and dental care researcher at the University of Washington School of Medicine. She notes that widely accepted research shows water fluoridation to be an effective disease-prevention measure, especially for people in communities with less access to dental care.
The EPA is currently deciding whether to appeal the district court’s order. But the Trump administration could sway the outcome by reversing any EPA decision made under outgoing president Joe Biden. And Kennedy’s rhetoric alone could persuade some individuals or communities to avoid fluoride-containing water. Since 2010 more than 170 U.S. cities, towns and counties have voted to halt fluoridation, according to one antifluoride group’s records. More are expected to follow suit: local lawmakers in Kentucky and Georgia recently sought to reverse their state’s fluoride mandate.
Below, Scientific American wades into the history and science of fluoridated drinking water by addressing some common questions.
Why do public health agencies recommend water fluoridation?
Towns and cities across the U.S. began adding fluoride to drinking water in the late 1940s, after studies of thousands of kids showed that communities with naturally occurring low levels of fluoride in their water supply experienced dramatically less tooth decay. The mineral—which is found in rocks, soil and water—prevents and repairs enamel erosion caused by oral bacteria. Today water utilities dissolve trace amounts of one of three fluoride-containing chemical additives in tap water. The U.S. Centers for Disease Control and Prevention’s recommended concentration is 0.7 milligram of fluoride per liter of water (an amount that is equivalent to about three drops of liquid per 55-gallon barrel). Facilities are required to monitor and report fluoride levels on a daily and monthly basis.
Fluoridating city water supplies initially slashed kids’ cavity rates by 50 to 70 percent and lowered adults’ rates by 20 to 40 percent, vastly reducing tooth pain, infection and loss. But now that toothpaste and beverage companies also add fluoride to their products, the benefits of community water fluoridation have decreased: several credible studies estimate that fluoridated water now reduces child and adult tooth decay by about 25 percent. The CDC and the American Dental Association emphasize that this still remains a significant benefit—and meaningfully shrinks dental health disparities.
A 2022 KFF poll found that dental services were the most common form of health care that adults put off because of high costs. Today at least 68.5 million Americans lack dental insurance, according to a 2023 survey by the CareQuest Institute for Oral Health. Having multiple fluoride sources offers peoples’ teeth much needed protection, says Susan Fisher-Owens, a University of California, San Francisco, Medical Center pediatrician, who studies barriers to children’s dental health. For people who cannot regularly access fluoride-containing dental products, fluoridated tap water provides a crucial—and cost-effective—baseline amount of the mineral. “The beauty of community water fluoridation is that it’s equal access,” she says.
Can fluoridated water pose risks to health?
In children who are still developing mature teeth, chronic fluoride overexposure can cause dental fluorosis, a condition that disrupts the uniform color and texture of enamel. Mild and moderate cases include harmless, albeit unattractive, white streaks or patches. Severe cases cause more conspicuous reddish-brown stains and pitted enamel, which can raise the risk of tooth decay.
To prevent severe dental fluorosis, the EPA requires public water systems to warn community members when their water sources exceed a fluoride level of two milligrams per liter (2 mg/L). That is around three times higher than the 0.7 mg/L concentration recommended by the HHS. Fluoride also appears in some foods, beverages and dental products but at small amounts that do not meaningfully contribute to a risk for dental fluorosis—except in cases where children regularly swallow large amounts of toothpaste. (Cute marketing and candylike flavors can sometimes encourage this.)
At extremely high concentrations—around twice the level that causes severe dental fluorosis—fluoride can accumulate in bones, weakening them and causing joint pain. But skeletal fluorosis is exceedingly rare in the U.S., which bans public water supplies from containing such high concentrations.
An apparent association between excessive fluoride exposure and lower IQ scores in children emerged in the 1990s and early 2000s from studies of rural villages in China, where wells had fluoride levels high enough to damage bones. But such findings do not apply to U.S. communities, which allow far less fluoride in water. The studies were also small and poorly designed, failing to account for pervasive contaminants produced by burning coal and peat. Continued research could not identify a clear mechanism that explains how fluoride might damage the developing brain. This prompted many scientists to question the link, Lewis says.
Then, in 2019, a JAMA Pediatrics study on pregnant people in Canada raised concerns about fluoride levels close to those that are currently recommended in the U.S. The small study found that if participants had higher fluoride levels in their urine during pregnancy (around 0.4 mg/L) and gave birth to a boy, on average, their son had slightly lower IQ test scores by the time he was three to four years old. (This finding did not apply to daughters.) But fluoride levels in a pregnant person’s urine do not indicate how much of the mineral that individual or their embryo or fetus actually takes in, explains Loc Do, an oral epidemiologist at University of Queensland in Australia, who wasn’t involved in the paper. The researchers also neglected to administer IQ tests in a standardized way, potentially skewing their results, and did not examine other factors correlated with a child’s IQ, such as maternal breastfeeding.
These studies still roused alarm, leading the HHS’s National Toxicology Program (NTP) to launch a review of the science in 2016. Its report, released in August 2024, claimed to have determined, “with moderate confidence,” that fluoridated water at concentrations of 1.5 mg/L—twice the average level found in U.S. water supplies—harms children’s IQ. (The report’s authors noted that the review did not address currently recommended exposure levels or “assess the benefits of the use of fluorides in oral health or provide a risk-benefit analysis.”)
But before it was even released, the agency’s report twice failed to pass scientific review from the National Academies of Sciences, Engineering, and Medicine, an independent research body. The most recent edition skipped independent review. The American Dental Association and the American Academy of Pediatrics criticized the latest report for generating conclusions from a small and weak body of research—and for omitting much larger studies that showed no neurocognitive threat at all from community water fluoridation.
“I wish we could put the genie back in the bottle on NTP,” says Steven Levy, a dental health care researcher at the University of Iowa. Despite having “some fundamental flaws,” the agency’s report has swayed many laypeople and some scientists who are unfamiliar with fluoride research. “Coming from such a well-regarded National Institutes of Health organization gives [the report] more credibility than it should have,” he says.
As a case in point, Do recently led a rigorous study of more than 2,500 kids in Australia that found that drinking water with fluoride as concentrated as 1.1 mg/L didn’t negatively affect children’s cognitive, emotional or behavioral development in their first five years of life. And a 2023 meta-analysis by Fisher-Owens and other dental experts, tasked with the same work as the National Toxicology Program, concluded that fluoride exposures up to 1.5 mg/L had no measurable effect on children’s IQ.
What might happen if more people or local governments reject water fluoridation?
Studies show communities that cease water fluoridation generally see more cavities in kids—and consequently incur higher dental bills. But the extent to which fluoride removal affects a population’s health varies because of factors such as diet and local dental practices.
After Israel nixed water fluoridation in 2014, for example, kids aged three to five required twice as many dental procedures as before. A comparison of two cities in Alberta, meanwhile, found that, among second-graders who grew up without any exposure to fluoridated water, the prevalence of cavities was 10 percent higher than that of their neighbors who were exposed. And children in Alaska who were younger than six years old and on Medicaid (the federal-state insurance program that covers most people with low incomes) developed an average of one additional cavity per year, requiring $300 more in dental care.
Public health researchers expect the brunt of fluoride removal to fall on people with low incomes, pre-existing dental conditions, or physical or cognitive disabilities. Levy believes that many healthy people would likely be able to maintain adequate dental health or to afford occasional cavity treatment, but he emphasizes that marginalized people tend to have fewer prevention and treatment options for tooth decay. Socioeconomic barriers can make it difficult for a person to regularly brush and floss their teeth, maintain a healthy diet or access dental care.
Local governments could mitigate negative health outcomes by distributing free toothbrushes, toothpaste tubes and bottles of fluoridated water to people who request them. Without coordinated action, however, people in communities that remove fluoride from the public supply will need to take more diligent care of their teeth.
Experts underscored the importance of brushing twice a day with fluoridated toothpaste, limiting sugar intake, particularly in the form of sodas and juices, and consulting a dentist or pediatrician about additional preventative measures. The U.S. Preventive Services Task Force—an independent panel of primary care experts—currently recommends that children under age five who do not have access to sufficiently fluoridated water receive oral fluoride supplements. Both children and adults can also benefit from receiving regular fluoride varnishes (a temporary enamel coating of highly concentrated fluoride) or plastic sealants (a semipermanent protective layer for tooth surfaces and crevices) at the dentist’s office.
Some specialized water filtration methods, such as reverse osmosis and the use of activated alumina, are designed to capture lead and other contaminants and can also sift out fluoride. (Common activated carbon filters such as Brita and Pur filters do not remove the mineral.) Experts say drinking only filtered or purified water may potentially cause insufficient fluoride intake, but occasional use isn’t a health concern.
Some dental products do not contain fluoride, such as hydroxyapatite toothpaste, which is approved in Canada and Europe.* Hydroxyapatite has received some hype in American media outlets, and small and limited studies show it to be similarly effective to fluoride toothpaste. Other experimental fluorideless toothpastes, however, have shown positive results that aren’t replicated in larger trials, says Gary Slade, a dental health epidemiologist at the University of North Carolina Adams School of Dentistry. “Maybe in five years, I’ll be giving [hydroxyapatite] a thumbs-up,” Slade says. “For now, I’d like to see some more studies.”
Public health experts also worry the current political frenzy around fluoride could feed more misinformation about effective health practices—including vaccinations. “Uncritical acceptance of these methodologically deficient studies will only encourage more poor-quality studies,” says Jay Kumar, a retired epidemiologist, who co-authored the 2023 meta-analysis. “If we keep perpetuating bad science, people are going to stop trusting government reports.”
*Editor’s Note (12/2/24): This sentence was updated after posting based on clarification from Fisher-Owens.
