Fluoride in saliva and in the oral mucosa

The fluoride in toothpaste does not disappear from the mouth immediately after brushing.
This study carried out in humans directly measured fluoride concentrations in saliva and in the oral mucosa after brushing with 1,450 and 5,000 ppm toothpastes. With the 1,450 ppm toothpaste, one hour after brushing, concentrations higher than the initial ones were still observed in both saliva and the oral mucosa.

Scientific study: Fluoride in Saliva and Oral Mucosa after Brushing with 1,450 or 5,000 ppm Fluoride Toothpaste (2019)

https://pubmed.ncbi.nlm.nih.gov/31307037/

How long does fluoride remain in saliva?

After brushing, the fluoride concentration in saliva increases and subsequently decreases progressively. This study compares the salivary retention produced by different fluoridated toothpastes and allows us to observe how the concentration evolves during the hours following brushing.

Scientific study: research on salivary fluoride retention after the use of different fluoridated toothpastes.

https://pubmed.ncbi.nlm.nih.gov/2059973/

These studies do not in themselves demonstrate systemic exposure or its possible effects. They demonstrate something more specific: after brushing, fluoride remains for a time in saliva and in the soft tissues of the mouth.

The next question takes us beyond the oral cavity:

can fluoride reach other tissues in the body, including the brain?

FLUORIDE: WHAT WE KNOW AND WHAT WE DON'T KNOW

Fluoride is used in dentistry for its anti-caries effect, and there is extensive scientific literature supporting this benefit.

But benefit and absolute absence of risk are not the same question.

On this page we want to examine another issue: what we know about our exposure to fluoride, what the studies show, and what questions remain open.

WHAT IS OUR TOTAL FLUORIDE EXPOSURE REALLY?

For a substance to exert certain effects directly on the brain, one of the fundamental questions is whether it can reach brain tissue by crossing the blood-brain barrier.

Experimental studies in animals indicate that fluoride can do so, although the barrier limits its diffusion.

In a study carried out on rats using fluorine-19 nuclear magnetic resonance, researchers detected fluoride directly in the brain after exposure. The brain concentration was approximately 20% of that found in the liver, a result that the authors interpreted as evidence of reduced, but not non-existent, diffusion across the blood-brain barrier.

Study: Uptake and life time of fluoride ion in rats by 19F-NMR (1993)

https://pubmed.ncbi.nlm.nih.gov/8345784/

Fluoride in the hippocampus

Another experimental study directly analysed the fluoride concentration in the hippocampus of rats subjected to subchronic exposure to sodium fluoride.

The researchers observed an increase in fluoride concentration in the hippocampus related to the dose administered and concluded that, in this experimental model, fluoride could cross the blood-brain barrier and accumulate in brain tissue.

Scientific study: Studies on fluoride concentration and cholinesterase activity in rat hippocampus.

https://pubmed.ncbi.nlm.nih.gov/14761523/

What does the body of experimental research show?

A review of the experimental literature published in 2022 likewise describes the passage of fluoride across the blood-brain barrier and its presence in different brain regions in experimental models. The review also analyses various proposed mechanisms of neurotoxicity.

Review: Fluoride Induced Neurobehavioral Impairments in Experimental Animals: a Brief Review (2022).

https://pubmed.ncbi.nlm.nih.gov/35488996/

Does this mean that the habitual use of a fluoridated toothpaste causes brain damage in humans? No. These studies do not demonstrate that.

They demonstrate something different and much more specific:

in animal models, the blood-brain barrier does not constitute an absolute barrier to fluoride, and it can reach brain tissue.

What relevance this fact has for habitual human exposures, especially when all sources of exposure are considered together, is a separate question that must be analysed in the light of the available epidemiological studies.

AND WHAT DO STUDIES IN HUMANS SHOW?

In 2025, a systematic review and meta-analysis published in JAMA Pediatrics, based on 74 epidemiological studies, found an association between higher fluoride exposure and lower IQ scores in children.
The researchers themselves warn, however, that there is uncertainty regarding lower exposures and that an epidemiological association does not by itself demonstrate causality.
The United States National Toxicology Program reached an equally nuanced conclusion: there is moderate-confidence evidence of an association between higher fluoride exposures and lower childhood IQ, but the available data do not allow us to determine whether the same occurs at the concentrations habitually used to fluoridate water.

Systematic review and meta-analysis published in JAMA Pediatrics

In 2025, JAMA Pediatrics published a systematic review and meta-analysis of 74 epidemiological studies on fluoride exposure and childhood IQ.

In the analysis of studies that had individual exposure measurements, an increase of 1 mg/L of urinary fluoride was statistically associated with a mean decrease of 1.63 IQ points. When the analysis was limited to studies considered to be at low risk of bias, the associated decrease was 1.14 points.

https://jamanetwork.com/journals/jamapediatrics/fullarticle/2828425

The authors found an inverse association between fluoride exposure and childhood IQ, but pointed out an important limitation: when exposure was estimated solely through the fluoride concentration in water below 1.5 mg/L, the data were limited and the dose-response relationship remained uncertain.

https://pmc.ncbi.nlm.nih.gov/articles/PMC11877182/

Scientific study: Fluoride Exposure and Children's IQ Scores: A Systematic Review and Meta-Analysis (2025).

Consult the full study in JAMA Pediatrics

What did the National Toxicology Program conclude?

In 2024, the United States National Toxicology Program (NTP) published its systematic review on fluoride, neurodevelopment and cognition.

Its conclusion was that there is moderate confidence in the scientific evidence of an association between higher fluoride exposures — for example, exposures approximated by concentrations in water above 1.5 mg/L — and lower childhood IQ.

https://ntp.niehs.nih.gov/research/assessments/noncancer/completed/fluoride

The NTP itself introduces a fundamental qualification: the available data do not allow us to determine whether low concentrations such as the 0.7 mg/L recommended for water fluoridation in the United States produce a negative effect on childhood IQ. An association, moreover, does not by itself demonstrate causality.

https://ntp.niehs.nih.gov/research/assessments/noncancer/completed/fluoride

But the report also points out something particularly relevant to the question we posed at the beginning of this page: total exposure does not come solely from water. It can vary according to other sources, including dental products, food and beverages. For this reason, a person may have a total exposure higher than that suggested by the fluoride concentration in their water alone.

https://www.ncbi.nlm.nih.gov/books/NBK606067/

Scientific report: NTP Monograph on the State of the Science Concerning Fluoride Exposure and Neurodevelopment and Cognition: A Systematic Review (2024).

Consult the official report of the National Toxicology ProgramA