When Frederick McKay graduated from the University of Pennsylvania’s Dental School in 1900, he had no idea that his new dental practice would lead to one of the most significant public health discoveries of the 20th century.
Setting up shop in Colorado Springs, McKay soon noticed something unusual — many residents had mottled brown stains on their teeth. It looked as if they had all been eating chocolate candy (but there were no telltale Hershey’s wrappers sticking out of their pockets).
Curious, McKay began investigating, and his findings caught the attention of other dental researchers. Eventually, similar cases were identified in communities across the country. Public health experts tested soil and water samples, and in 1931, the culprit was finally identified: high levels of naturally occurring fluoride in the local water supply.
Then came the second surprise — people with these stained teeth also had far fewer cavities. It turned out that fluoride, while causing excessive discoloration, also strengthened tooth enamel, making teeth more resistant to decay. This discovery paved the way for fluoride’s addition to dental products such as toothpaste and mouthwash and, eventually, to the public water supply.
As of this writing, the US Centers for Disease Control and Prevention (CDC) considers water fluoridation one of the 10 greatest public health achievements of the 20th century. When fluoridation programs became widespread in the US after 1945, the rates of tooth decay among Americans soon plummeted by about 25%.
More recently, however, water fluoridation has become extremely controversial. While it’s clear that fluoride benefits dental health, the chemical doesn’t just end up on your teeth when you drink it; it affects your entire body. And there’s increasing concern about the effects of fluoridation on pregnant women and children.
It’s also worth considering that the broad availability of fluoride-containing dental care products may render the continuation of water fluoridation unnecessary.
In this article, we’ll separate fluoride fact from fiction and identify its known risks and benefits so you can make the right decisions for your health and that of your loved ones.
What Is Fluoride and How Is It Used?
Fluorine is a highly reactive gas at room temperature and is one of the halogens (like chlorine and iodine). Fluoride is the ionic form of fluorine, and it is produced when fluorine gains an electron. This electron turns fluoride into a stable ion that forms compounds rather than existing as a gas.
Fluoride is used largely to promote dental health. Dentists apply it during regular checkups, municipalities add it to the water to improve public dental health, and consumer products like toothpaste, mouthwash, and floss often contain fluoride.
Fluoride is also found in some supplements, pesticides, cleaning products, and medical imaging scans, such as PET scans. It’s also used to manufacture Teflon, steel, and aluminum.
Reported Benefits of Widespread Fluoride Use
Given the widespread use of fluoride in the water supply (over 70% of US residents receiving public water get fluoridated water), it’s reasonable to ask why. What are the benefits of fluoridated water according to public health officials who promote the practice?
There’s one apparent benefit of fluoride: dental health.
Topical Fluoride and Dental Health
As we’ve seen from the Colorado Brown Stain incident, fluoride was shown to strengthen tooth enamel (the hard outermost surface of teeth, which is harder than bone and may even be harder than not tapping your feet at a Taylor Swift concert), thus preventing tooth decay.
This finding isn’t in question; multiple studies have shown (and continue to show) that fluoride prevents tooth decay and improves dental health in children. A 2015 study out of Bosnia and Herzegovina found that six months of topical fluoride treatment significantly improved dental health in a group of children compared to controls who were not given the treatment.
Two comprehensive reviews by Cochrane (an organization largely respected by medical researchers for its impartiality and rigor) — one in 2003 and the other in 2019 — found that fluoride in toothpaste reduces tooth decay.
The 2003 meta-analysis examined 70 studies involving more than 42,000 children, and the 2019 review analyzed data from almost 100 studies involving over 60,000 participants. In both cases, researchers concluded that fluoride toothpastes are significantly more effective in preventing cavities than non-fluoride toothpastes.
I want to point out something here. These studies look at the effectiveness of fluoride in toothpaste. They don’t say anything about fluoridated water. So what about the evidence for fluoridation of the public water supply? Is it as robust and conclusive?
Fluoridated Water and Dental Caries
When we look at the rates of dental caries (the process of enamel decay) and cavities (the holes caused by this process), it’s clear that these rates declined when communities began fluoridating their water.
A 2013 study examined the impact of fluoridated drinking water on reducing cavities in Australian adults, comparing those born before 1960 (whose water wasn’t fluoridated) with those born between 1960 and 1990 (whose water did contain fluoride). The results showed that individuals with over 75% lifetime exposure to fluoridated water had fewer dental issues, indicating that fluoridated water did reduce cavities.
A 2018 study similarly examined the impact of fluoridated drinking water on dental health in US children and adolescents. Again, those in areas with fluoridated water experienced significantly fewer cavities. And the younger the child, the greater the protective effect. Specifically, children aged 2 to 8 had about 30% fewer cavities in their primary (baby) teeth, while those aged 6 to 17 saw a 12% reduction in cavities in their permanent teeth.
Since 1962, the US Public Health Service has recommended adding fluoride to drinking (tap) water to reduce the risk and severity of dental caries. They’ve identified 0.7 milligrams per liter as the concentration that maximizes fluoride’s oral health benefits while minimizing potential harm.
Other major health organizations, such as the World Health Organization, and professional dental groups, such as the International Association for Dental, Oral, and Craniofacial Research and the American Dental Association, also endorse fluoride use in water.
The Community Preventive Services Task Force reported back in 2000 that water fluoridation caused an average decrease in dental caries of almost 30% in children ages 4 to 17 years compared to control groups whose water was not fluoridated.
However, based on the Cochrane reviews referenced in the previous section, no reputable studies have aimed to determine the effectiveness of water fluoridation for preventing caries in adults.
And when we look at a major public health initiative, we have to consider both potential benefit and potential harm. Regarding the latter, controversy has surrounded water fluoridation from the beginning.
The Debate Over Public Water Fluoridation
Despite evidence that fluoride in the water supply can preserve tooth enamel in children, it’s not universally accepted that the benefits outweigh the potential risks. Most developed countries do not fluoridate their water.
For one thing, there are concerns that people can get overexposed to fluoride, especially if they already get it from their dental hygiene products.
And there’s a big difference between topical application of fluoride (from toothpaste, mouthwash, or floss) and drinking it. When you drink fluoridated water, that fluoride affects your body systemically. In the UK and other countries, the advice on fluoridated dental products is to avoid swallowing them, especially for children.
Possible Risks of Water Fluoridation
So, what are the risks that prompted the fluoride debate? Let’s look at the major ones.
Dental and Skeletal Fluorosis
We’ve seen that too much fluoride in water when teeth are growing in childhood can lead to discoloration, which is known as dental fluorosis.
Fluoride can also become concentrated in your bones (a condition known as skeletal fluorosis), stimulating bone cell growth, altering bone tissue structure, and weakening your skeleton.
Neurological Effects of Fluoride
Most studies showing harmful neurological effects were conducted on laboratory animals, like this 2019 experiment on baby rats that showed impaired memory and measurable changes in their brains. (Our view on the use of animals in medical research is here.) Fortunately, scientists are not allowed to conduct research like this on humans. However, they can run “natural experiments” in populations where different communities have different levels of exposure to fluoridated water.
A 2012 review analyzed 27 studies, mainly from China, and discovered a consistent pattern of lower intelligence scores among children exposed to higher fluoride levels.
A 2025 paper published in JAMA Pediatrics has rekindled debate over fluoridation — some of it quite heated. Researchers analyzed 74 studies (mainly from China and India and some from Canada, Denmark, New Zealand, Iran, Mexico, Pakistan, and Spain). They found that children in high-fluoride areas may have significantly lower IQ scores than those who live in low-fluoride areas.
For perspective, water fluoride concentrations in China and India are considerably higher than in the US water supply.
The potential effects of fluoridated water on the brain are not limited to memory and intelligence. A 2021 study out of Canada found that a one milligram per liter increase in the fluoride level in tap water raised the odds of a diagnosis of attention deficit and hyperactivity disorder (ADHD) in children by more than 6 times. (For context, the amount generally added to US tap water is 0.7 milligrams per liter.)
Fluoride and Thyroid Function
Other bodily systems and organs may also be harmed by fluoridated water. A 2024 systematic review found a potential association between chronic high levels of fluoride exposure and thyroid damage.
That bolstered confidence in the findings of another older study, which found that Canadian adults with moderate-to-severe iodine deficiencies may be at an increased risk for underactive thyroid gland activity when exposed to higher fluoride levels.
Is Fluoridated Water Necessary for Dental Health These Days?
The first fluoridated toothpaste appeared on store shelves in the US in 1956. (For trivia buffs, the brand was Crest.) Since the widespread availability of fluoride toothpaste and other fluoridated products, dental cavities have decreased in countries with and without water fluoridation.
Proponents of water fluoridation contend that the practice has reduced oral health disparities. They say it ensures everyone gets a consistent dose of fluoride, helping to lower cavity rates across the board.
In fact, a 2024 study published in the prestigious journal Nature found that US communities with more Hispanic or Latino residents had higher levels of fluoride in the water supply than predominantly white areas. But given what we know about bones, brains, and thyroids, that might be worsening the health of these communities.
Issues With Informed Consent
Given the evidence of potential neurological harm that may impair children’s cognitive development and increase the risk of ADHD, there’s a serious ethical issue here. Namely, parents can’t give or withhold consent to the fluoridation of their children.
Most US households get fluoridated water when they turn on their taps. Globally, over 400 million people in 25 countries have community water fluoridation.
To be clear, we treat water for many reasons: to kill pathogens, harden or soften it, and filter out harmful or bad-tasting chemicals. But fluoridation is categorically different. Unlike all other water treatment processes, fluoridation does not treat the water but the person consuming it, which is a form of mass medication.
According to the FDA, fluoride is a drug, not a nutrient, when used to prevent disease. For this reason, most Western European nations have rejected water fluoridation. In their view, the public water supply is not an appropriate place to add drugs.
What You Can Do: Take Action for Your Health
Given all this uncertainty, I won’t make any definitive proclamations about whether fluoride is inherently safe here. But I do have opinions, which I hope will help you make up your own mind on the matter.
One of my takeaways is that fluoride in toothpaste and dental floss is probably helpful in cavity prevention for most people. As long as you use small amounts (the size of a pea, as my toothpaste tube informs me), avoid swallowing it, and rinse your mouth well, you’ll likely absorb only minimal amounts into your body.
Water fluoridation may benefit your teeth, but it also may negatively affect other areas of your body, including your brain. If you regularly use fluoridated toothpaste and/or mouthwash, the risks of consuming fluoride in water may outweigh any potential benefits. And that may be especially true for adults with fully-formed tooth enamel.
Tips for Managing Fluoride Exposure
So, what can you do if you decide that fluoridated water isn’t worth the risk? It’s not like candy or soda, that you can just walk past in the grocery store and not toss into your shopping cart.
1. Check for Fluoridation in the Water Supply
If you live in many parts of the US, you can check whether your city fluoridates its water using the CDC’s “My Water’s Fluoride” online database. (Note: several states, including New York, New Jersey, New Mexico, Arizona, Washington, Wyoming, Montana, and South Dakota, declined to share this data with the CDC.) You may also be able to contact your local water provider or district to inquire.
2. Filter Your Water
If your water is fluoridated and you wish it weren’t, you may want to invest in a water filtration system. Not all systems are equally (or even at all) effective in removing fluoride; the best ones are reverse osmosis units and water softeners.
For our recommendations on the best home water treatment systems, check out our article on Drinking Water Treatment: When It’s Necessary & What Your Options Are.
3. Check Personal Care Products and Vitamins
You can also check if your personal care products and supplements contain fluoride. If they do, make sure that your children aren’t overusing them.
- For ages three to six, no more than the size of a pea of fluoride-containing toothpaste should be smeared on a child’s toothbrush.
- Before age three, when children are likely to swallow a decent amount of toothpaste, parents should smear no more than the size of a grain of rice on a child’s toothbrush.
- For children younger than two, consult your doctor or dentist before using fluoride toothpaste or other fluoride products.
Also be sure to check the labels of multivitamins, which may also contain sodium fluoride.
4. Check for Fluoride Content in Other Dietary Staples
Some countries have added fluoride to grocery staples such as table salt and milk. Salt is often fluoridated in Caribbean and Latin American countries, while you’ll encounter fluoridated milk in Bulgaria, Thailand, Chile, China, Peru, and parts of the Russian Federation.
For reference, here are the Daily Tolerable Upper Intake Levels for Fluoride, according to the US National Institutes of Health:
| Age | Male | Female | Pregnancy | Lactation |
| Birth to 6 months | .07 mg | .07 mg | ||
| 7–12 months | 0.9 mg | 0.9 mg | ||
| 1–3 years | 1.3 mg | 1.3 mg | ||
| 4–8 years | 2.2 mg | 2.2 mg | ||
| 9–13 years | 10 mg | 10 mg | ||
| 14–18 years | 10 mg | 10 mg | 10 mg | 10 mg |
| 19+ years | 10 mg | 10 mg | 10 mg | 10 mg |
Stay Informed on Fluoride
Fluoride remains a complex and controversial topic, balancing dental health benefits with potential health concerns. While it has played a crucial role in reducing tooth decay, the widespread availability of fluoridated dental products and evolving public health data call for reevaluating its necessity — and its ethical implications — in water supplies. As research continues to unfold, informed personal decisions, such as monitoring fluoride exposure and using appropriate filtration systems, can help people make conscious and intentional choices.
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Tell us in the comments:
- Is your tap water fluoridated?
- Do you have a water filter?
- Do you choose oral health products with or without fluoride?
Featured image: istock.com/Irina_Timokhina
