Basically, no. (Updated 2022-01-20: Additional sources, footnotes; minor corrections/edits.)

I am not a medical professional, this article is the result of personal research, and it should not be considered medical advice. Additionally, this article is written for American audiences who are concerned with fluoride in drinking water. Unfortunately, fluoride exposure is far more common in less privileged countries (especially India and China)^{1, 15}. In these countries, it is not from drinking water.

I’m going to get straight to the point: The worst danger for the average person is very unlikely joint pain and brittle bones. This is called skeletal fluorosis¹, and is caused by the body absorbing too much fluoride into bone tissue, which causes it to be brittle. It is difficult to consume enough fluoride to cause skeletal fluorosis – unless you’re eating toothpaste.

For children/teens (6-17)², there is an increased risk of dental fluorosis, which is discoloration of teeth, and very rarely structural damage can also occur (in less than 0.25% of the population³). This is because children and teens are more likely to swallow toothpaste, and more likely to use too much toothpaste. See the “How To Use Toothpaste” section below for more information, and please do read it because most people use too much toothpaste and don’t know it (including me before researching this article).

My Bias & My Sources’ Bias

I choose to use the worst possible case as presented from available data, because that level of caution tells me if danger is even a possibility. As a result, most of the sources I am using are from organizations against the use of fluoride in drinking water^{4, 6, 15, 17}, and likely includes conspiracy theorists.

Ironically, the worst case data presented is that fluoride is not dangerous to the average person, and the benefits of fluoridated water outweigh the risks. This is despite several of my sources not distinguishing between dental and skeletal fluorosis^{4, 6, 15}. Dental fluorosis is almost entirely harmless, while skeletal fluorosis can be crippling.

How Much Fluoride is Dangerous?

This is a difficult question to answer, and the average person does not need to worry about it. If you have poor kidney function, you should probably talk to a doctor about it. It is also more likely to affect you if you have a calcium or vitamin D deficiency⁵.

Most studies I looked at are of populations with medical problems that leave them susceptible to fluorosis. The lowest consumption I can possibly link to the average person developing any kind or amount of fluorosis is 10mg/day every day for 6 months^{4, 15}, and this estimate is based on the most rapid onset fluorosis study I could find combined with a more reasonable estimate for the magnitude of consumption required⁶.

In order to consume 10mg/day of fluoride, one would need to drink 8 liters of highly fluoridated water^{7, 14}, or eat 4 liters of raisins^{8, 17}, or eat around 3-5 times as much maximally fluoridated toothpaste as should be used per day⁹… And you would have to do these every day for 6 months or longer.

How Much Fluoride Am I Consuming? A Worst Case

Dental fluorosis occurs while teeth grow, and is the most common risk of fluoride. I set out to figure out the worst case consumption for a child around age 6, but these numbers can be easily extended to older or younger people.

Children 4-11 years old consume 2-2.2mg/day fluoride, of which 0.2-0.3mg is from toothpaste¹⁰. Assuming the worst case in these factors, this means children are getting 1.9mg/day from non-toothpaste sources, and spitting out 2.4mg/day from their toothpaste. But this is not the worst case. This estimate means children are drinking less than a liter of water per day and no food with fluoride in it, which is definitely not true.

A child 4-8 years old should be consuming 1.18 liters of water per day¹¹, and is definitely getting fluoride from food as well^{8, 17}. To make the worst case, I’m going to add 1.18 liters of maximally fluoridated water (1.42mg), a liter of the most fluoridated food (raisins, 2.34mg), and assume they’re using twice as much toothpaste as they should, using maximally fluoridated adult toothpaste, brushing twice a day, and swallowing it all. That’s 6mg/day from toothpaste alone!

Altogether? 9.76mg/day of fluoride, which is not good, but amazingly, is still below the worst threshold I could possibly link to fluorosis (10mg/day).

The most important take-away from this is: Don’t swallow toothpaste. Don’t use too much toothpaste.

How To Use Toothpaste

This is actually fairly simple, but please consult with a dentist, especially for young children. A “pea-sized” dollop is all you need. Children are at the highest risk of having dental problems, and so the right balance for them is most difficult.

If one has a hard time spitting or rinsing out toothpaste, consider finding a toothpaste with lower fluoride concentrations. This is more common in children’s toothpaste, but there is significant overlap in fluoride concentrations between adult and child toothpaste¹².

(I was under the impression that children’s toothpaste should have lower fluoride than adult toothpaste, but lower concentrations are associated with worse dental outcomes, while higher concentrations are more likely to only cause mild fluorosis. Additionally, fluorosis matters far less for a child’s first set of teeth – and its presence or lack thereof can be used to guide changes in their fluoride use.)

Sources, References, Footnotes

1. Wikipedia states this with a dead link to an article from UNICEF. However, multiple sources of similar information can be found via search. In the interest of time, I did not research more details.
2. I am combining data from many sources to state the range of children at increased risk. Different sources give different ranges, and are primarily focused on pre-teen ages. Dental fluorosis can occur any time teeth are growing, and thus this includes teens.
3. Prevalence and Severity of Dental Fluorosis in the United States, 1999-2004. (CDC)
4. Fluoride Action Network discusses and links to many studies. However, they do not distinguish between dental and skeletal fluorosis – instead claiming that all fluorosis cases are dangerous and crippling. Additionally, they do not clarify which studies are of a sub-population (such as the many studies on kidney disease and kidney failure), and they do not clarify the difference between very rare occurrences and reasonable risks to the average person.
5. Fluoride does not replace calcium in enamel (for teeth) and bone, but a lack of calcium increases how much fluoride is absorbed by enamel and bone.
6. Estimated Thresholds For Fluorosis. Warning: This page appears to be misleading, as it is part of the Fluoride Action Network⁴, and intermixes studies across a wide range of locations & causes without clearly distinguishing between types of fluorosis.
7. Water has been fluoridated to 0.7-1.2mg/L. At the maximum concentration, one would need to consume 8.33 liters per day to receive 10mg/day, which is not really possible¹⁴.
8. FoodData Central. (USDA) (Originally, I used a different source¹⁷, but they also promote unscientific claims.)
9. Adult toothpaste contains 1,000-1,500mg/L fluoride, adults should use no more than a “pea-sized” amount of toothpaste (approximately 1mL)^{citation needed}, which means that swallowing adult toothpaste gives 1-1.5mg fluoride per swallow.
10. Fluoride – Health Professional Fact Sheet. (NIH)
11. HealthyChildren.org’s page about hydration.
12. Study highlights fluoridated toothpaste use in children.
13. 1 ppm is equivalent to 1 mg/L. For consistency, I used mg/L within this article.
14. Drinking more than 1 L/hr of water for more than 2 hours leads to water toxicity. It is likely one could die from water toxicity before they could consume enough fluoride to cause harm.
15. Most studies “linking fluoride to negative health effects” are in India and China and based on high levels of contamination of multiple materials. These do not distinguish between lead, arsenic, and other toxins more likely to be the cause of these issues. Note: I did not do this analysis myself, and am relying on Professor Dave.
16. In 2015, the US Department of Health & Human Services recognized that fluoride should be limited to 0.7mg/L for an optimal balance between dental protection and risk of causing dental fluorosis.
17. Largest List of Foods That Contain Fluoride. Warning: This website is promoting pseudoscientific claims. Specifically, they claim to be able to remove fluoride from one’s body in 28 days, which is impossible due to how it bonds with bone and how slowly bone is reformed.