The short answer: Fluoride helps enamel repair itself after acid attacks and makes it harder for decay to start. Brushing twice a day with fluoride toothpaste is the best-proven way to use it: high-certainty evidence shows it prevents cavities compared with toothpaste without fluoride. Varnish, gels and supervised rinses add protection for people at higher risk. The main side effect is mild white marks on children’s teeth (fluorosis) from swallowing too much while teeth form, which the right amount of toothpaste helps prevent. Concerns about IQ center on levels above 1.5 mg/L in drinking water, about twice the US level.
The World Health Organization considers adequate fluoride exposure essential for preventing tooth decay and encourages twice-daily brushing with fluoride toothpaste (World Health Organization, 2025). At the same time, questions about fluoride’s safety have grown louder, and in 2025 the US Food and Drug Administration narrowed who should take fluoride supplements (U.S. Food and Drug Administration, 2025).
This guide explains how fluoride works, how much your toothpaste should contain, which professional treatments help, who needs supplements, and what the evidence says about fluorosis and other safety concerns.
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How does fluoride protect your teeth?
Fluoride is a naturally occurring mineral found in water, soil, plants and many foods. It protects teeth mainly by helping enamel take back minerals after acid attacks (remineralization) and by slowing the loss of minerals that leads to decay (Featherstone, 2000). Even the low levels left in saliva after brushing shift the balance toward repair, and the rebuilt enamel contains fluoride in the form of fluorhydroxyapatite (ten Cate, 1999).
Fluoride can also inhibit bacterial enzymes (Featherstone, 2000), although the low levels in saliva after brushing do little to interfere with bacterial growth (ten Cate, 1999). Fluoride in drinking water works mainly the same way, through contact with teeth in the mouth, rather than by strengthening teeth before they come in (Featherstone, 2000). That repair process is why early decay can sometimes reverse; see can a cavity heal on its own?
How much fluoride should your toothpaste have?
A Cochrane review of 96 trials found high- and moderate-certainty evidence that toothpaste with 1,000 to 1,250 ppm or 1,450 to 1,500 ppm of fluoride reduces cavities in children and teenagers compared with toothpaste without fluoride, and that 1,450 to 1,500 ppm works slightly better than 1,000 to 1,250 ppm. In adults of all ages, 1,000 to 1,100 ppm toothpaste also reduced decay compared with non-fluoride toothpaste (Walsh et al., 2019).
In practice, that means a regular adult toothpaste with fluoride; the NHS advises adults to use one with at least 1,350 ppm (NHS, 2025). People at higher risk can get a prescription toothpaste or gel with 5,000 ppm (1.1% sodium fluoride), which the American Dental Association’s guideline lists among the options for stopping early decay, including on exposed roots (Slayton et al., 2018). Ask your dentist whether you need it.
How much toothpaste should children use?
The American Academy of Pediatric Dentistry recommends brushing twice a day from the first tooth, with a smear of fluoride toothpaste the size of a grain of rice until age 3 and a pea-sized amount from age 3 (American Academy of Pediatric Dentistry, 2025). The CDC adds that parents of children under 2 should check first with their doctor or dentist, and that children should be supervised and taught to spit rather than swallow (Centers for Disease Control and Prevention, 2024b). The small amounts matter because the choice of toothpaste for young children has to be balanced against the risk of fluorosis (Walsh et al., 2019). The parent’s guide to kids’ teeth covers brushing at each age.
Should you rinse after brushing?
No. Spit out the excess toothpaste but don’t rinse with water, because rinsing washes away the concentrated fluoride left on your teeth. For the same reason, the NHS advises using mouthwash, even a fluoride one, at a different time from brushing, such as after lunch (NHS, 2025). Our daily dental hygiene routine puts these steps together.
What professional fluoride treatments are there?
Fluoride varnish
Varnish is a concentrated fluoride coating painted onto the teeth. In a Cochrane review of 22 trials in children and teenagers, varnish reduced decayed, missing and filled surfaces by 43% in permanent teeth and 37% in baby teeth compared with placebo or no treatment, based on moderate-quality evidence (Marinho et al., 2013). The US Preventive Services Task Force recommends that primary care clinicians apply fluoride varnish to the baby teeth of all infants and children from the time the first tooth appears (US Preventive Services Task Force, 2021).
Fluoride gels
Gels are applied in trays or with a toothbrush, usually at a dental office or school program. A Cochrane review of 28 trials found that they reduced decay in children’s permanent teeth by 28% (moderate-quality evidence), with a smaller, less certain effect in baby teeth (Marinho et al., 2015).
Fluoride mouthrinses
Supervised, regular use of a fluoride mouthrinse by children and teenagers was linked to 27% fewer decayed, missing or filled tooth surfaces (Marinho et al., 2016).
Silver diamine fluoride
Silver diamine fluoride is a liquid painted onto decay to stop it. A 2024 Cochrane review concluded that it may help arrest decay in baby teeth and probably helps prevent new decay on exposed roots, but that the evidence for adults’ crowns is uncertain (Worthington et al., 2024).
Do children need fluoride supplements?
Most don’t. In 2021, the US Preventive Services Task Force recommended prescription fluoride supplements from age 6 months for children whose water supply is low in fluoride (US Preventive Services Task Force, 2021). In October 2025, however, the FDA recommended limiting fluoride tablets and drops to children 3 and older who are at high risk of tooth decay, such as those with past cavities and no fluoridated water (U.S. Food and Drug Administration, 2025). If that might describe your child, ask their dentist or pediatrician.
Does fluoride in tap water still help?
The CDC states that fluoridated water reduces cavities by about 25% in children and adults (Centers for Disease Control and Prevention, 2024a). A 2024 Cochrane review found a smaller benefit in studies carried out since 1975, when fluoride toothpaste came into wide use: about a quarter of a decayed, missing or filled baby tooth per child, based on low-certainty evidence that included the possibility of no benefit (Iheozor-Ejiofor et al., 2024). Our article on whether water fluoridation is safe covers the research and the latest US policy changes.
Is fluoride safe?
Dental fluorosis
Dental fluorosis, which usually appears as white flecks, spots or lines on the teeth, can develop when children swallow too much fluoride while their teeth are forming, especially in the first years of life (Buzalaf & Levy, 2011). In the United States it is mostly mild and cosmetic: it doesn’t affect how teeth work or cause pain, and moderate and severe forms are rare (Centers for Disease Control and Prevention, 2024b). At the 0.7 mg/L level used in US community water, an estimated 12% of people have fluorosis noticeable enough to be of cosmetic concern, according to low-certainty evidence from the Cochrane review’s 2015 analysis, which its 2024 update did not revisit (Iheozor-Ejiofor et al., 2024).
Children’s IQ
A 2024 review by the US National Toxicology Program found, with moderate confidence, that fluoride exposures above 1.5 mg/L in drinking water are consistently associated with lower IQ in children (National Toxicology Program, 2024). That is more than twice the 0.7 mg/L recommended for US community water, and the program found insufficient data to say whether 0.7 mg/L has any effect on IQ; it also didn’t assess fluoride’s benefits (National Toxicology Program, 2026). These questions concern swallowed fluoride, which is another reason to use the right amount of toothpaste for children and to spit rather than swallow.
What it means for you
For adults
Brush twice a day with a fluoride toothpaste of at least 1,350 ppm and spit without rinsing (NHS, 2025). If you get cavities often, have exposed roots or a dry mouth, ask about a 5,000 ppm prescription toothpaste (Slayton et al., 2018). The guide to how to prevent cavities covers the other steps.
For parents
Use a rice-grain smear until age 3 and a pea-sized amount from 3 (American Academy of Pediatric Dentistry, 2025), ask about fluoride varnish at checkups (US Preventive Services Task Force, 2021), and use supplements only if your child’s dentist or doctor recommends them (U.S. Food and Drug Administration, 2025).
If your water isn’t fluoridated
Fluoride toothpaste becomes even more important, and your dentist may suggest varnish or another topical treatment if your risk is high (Marinho et al., 2013; Walsh et al., 2019).
Questions to ask your dentist
- What is my cavity risk, and is my toothpaste strong enough?
- Would fluoride varnish or a prescription toothpaste help me or my child?
- Does my child need a fluoride supplement under the FDA’s new limits?
- Are these white marks fluorosis or early decay?
When to see a dentist
Book a dental visit if:
- You notice white, chalky or brown spots on your or your child’s teeth.
- You keep getting new cavities despite brushing twice a day.
- Your teeth are sensitive to sweets, cold or heat.
- Your child hasn’t had a dental visit by their first birthday.
For severe pain or swelling, see what to do in a dental emergency.
The bottom line
Fluoride helps enamel repair early acid damage, and brushing twice a day with fluoride toothpaste is the best-proven way to prevent cavities. Varnish, gels and supervised rinses add protection for children and people at higher risk, while supplements are now recommended only for some high-risk children aged 3 and older. Using the right amount of toothpaste and spitting rather than swallowing keeps the main side effect, mild fluorosis, to a minimum.
References
American Academy of Pediatric Dentistry. (2025). Policy on early childhood caries (ECC): Consequences and preventive strategies. https://www.aapd.org/globalassets/media/policies_guidelines/p_eccconsequences.pdf
Buzalaf MAR, Levy SM. (2011). Fluoride intake of children: Considerations for dental caries and dental fluorosis. Monographs in Oral Science, 22, 1–19. https://doi.org/10.1159/000325101
Centers for Disease Control and Prevention. (2024a). About community water fluoridation. https://www.cdc.gov/fluoridation/about/index.html
Centers for Disease Control and Prevention. (2024b). About dental fluorosis. https://www.cdc.gov/oral-health/about/about-dental-fluorosis.html
Featherstone JD. (2000). The science and practice of caries prevention. Journal of the American Dental Association, 131(7), 887–899. https://doi.org/10.14219/jada.archive.2000.0307
Iheozor-Ejiofor Z, Walsh T, Lewis SR, Riley P, Boyers D, Clarkson JE, et al. (2024). Water fluoridation for the prevention of dental caries. Cochrane Database of Systematic Reviews, 10(10), CD010856. https://doi.org/10.1002/14651858.CD010856.pub3
Marinho VCC, Worthington HV, Walsh T, Clarkson JE. (2013). Fluoride varnishes for preventing dental caries in children and adolescents. Cochrane Database of Systematic Reviews, 2013(7), CD002279. https://doi.org/10.1002/14651858.CD002279.pub2
Marinho VCC, Worthington HV, Walsh T, Chong LY. (2015). Fluoride gels for preventing dental caries in children and adolescents. Cochrane Database of Systematic Reviews, 2015(6), CD002280. https://doi.org/10.1002/14651858.CD002280.pub2
Marinho VC, Chong LY, Worthington HV, Walsh T. (2016). Fluoride mouthrinses for preventing dental caries in children and adolescents. Cochrane Database of Systematic Reviews, 7(7), CD002284. https://doi.org/10.1002/14651858.CD002284.pub2
National Toxicology Program. (2024). NTP monograph on the state of the science concerning fluoride exposure and neurodevelopment and cognition: A systematic review (NTP Monograph 08). https://ntp.niehs.nih.gov/publications/monographs/mgraph08
National Toxicology Program. (2026). Fluoride exposure: Neurodevelopment and cognition. https://ntp.niehs.nih.gov/research/assessments/noncancer/completed/fluoride
NHS. (2025). How to keep your teeth clean. https://www.nhs.uk/live-well/healthy-teeth-and-gums/how-to-keep-your-teeth-clean/
Slayton RL, Urquhart O, Araujo MWB, Fontana M, Guzmán-Armstrong S, Nascimento MM, et al. (2018). Evidence-based clinical practice guideline on nonrestorative treatments for carious lesions: A report from the American Dental Association. Journal of the American Dental Association, 149(10), 837–849.e19. https://doi.org/10.1016/j.adaj.2018.07.002
ten Cate JM. (1999). Current concepts on the theories of the mechanism of action of fluoride. Acta Odontologica Scandinavica, 57(6), 325–329. https://doi.org/10.1080/000163599428562
U.S. Food and Drug Administration. (2025). Ingestible fluoride drug products. https://www.fda.gov/news-events/public-health-focus/ingestible-fluoride-drug-products
US Preventive Services Task Force; Davidson KW, Barry MJ, Mangione CM, Cabana M, Caughey AB, et al. (2021). Screening and interventions to prevent dental caries in children younger than 5 years: US Preventive Services Task Force recommendation statement. JAMA, 326(21), 2172–2178. https://doi.org/10.1001/jama.2021.20007
Walsh T, Worthington HV, Glenny AM, Marinho VC, Jeroncic A. (2019). Fluoride toothpastes of different concentrations for preventing dental caries. Cochrane Database of Systematic Reviews, 3(3), CD007868. https://doi.org/10.1002/14651858.CD007868.pub3
World Health Organization. (2025). Oral health. https://www.who.int/news-room/fact-sheets/detail/oral-health
Worthington HV, Lewis SR, Glenny AM, Huang SS, Innes NP, O’Malley L, et al. (2024). Topical silver diamine fluoride (SDF) for preventing and managing dental caries in children and adults. Cochrane Database of Systematic Reviews, 11(11), CD012718. https://doi.org/10.1002/14651858.CD012718.pub2
References checked October 2026 · Editorial policy · Report a correction
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