Fluorine and Hydrogen Fluoride Explained: Hazards, Uses, Fluorite, Fluoride in Toothpaste, Dental Care, and Drinking Water

What Is Fluorine?

Fluorine is an element with the chemical symbol F and atomic number 9.
On the periodic table, it is classified as a Group 17
“halogen,” along with chlorine, bromine, iodine, and others.

At room temperature, elemental fluorine is a pale yellow gas
consisting of diatomic molecules with the formula F₂.

Fluorine gas is an extremely powerful oxidizing agent
and reacts with many metals, nonmetals, and organic compounds.

Therefore, in nature, fluorine generally exists not as F₂,
but as fluoride compounds combined with other elements.

“Fluorine” and “Fluoride” Are Strictly Different

In everyday life, expressions such as “fluoride toothpaste”
and “having fluoride applied at the dentist” are commonly used.

Chemically, however, these products do not contain
elemental fluorine gas F₂.

Most substances referred to as “fluorine” in dentistry
are actually fluoride compounds such as sodium fluoride.

What Is Hydrogen Fluoride?

Hydrogen fluoride is a compound consisting of hydrogen and fluorine,
with the chemical formula HF.

Hydrogen fluoride is highly soluble in water.
An aqueous solution of HF is called hydrofluoric acid.

Where Is Fluorine Found in Nature?

Because fluorine is extremely reactive,
it is rarely found in elemental form in nature.

A representative natural mineral is fluorite, or fluorspar,
whose main component is calcium fluoride (CaF₂).

Fluorite is an important natural resource
used to manufacture hydrogen fluoride and various fluorine compounds.

In particular, high-purity acid-grade fluorspar
is used as a primary raw material for hydrogen fluoride production.

In Which Countries Is Fluorite Mined?

China accounts for a very large share of global fluorite production.

China alone accounts for approximately 60% of global production
and therefore plays a very important role
in supplying raw materials for the fluorine chemical industry.

How Is Hydrogen Fluoride Produced?

Industrial hydrogen fluoride is produced mainly
from calcium fluoride contained in fluorite.

In the basic reaction,
calcium fluoride reacts with sulfuric acid
to produce hydrogen fluoride.

The hydrogen fluoride obtained is purified
and used as anhydrous hydrogen fluoride
or as hydrofluoric acid at various concentrations.

Why Is Fluorine So Highly Reactive?

Fluorine’s high reactivity is related
to its atomic size and electron configuration.

A fluorine atom has seven valence electrons,
and by accepting one more electron,
it reaches a stable closed-shell electron configuration.

Fluorine atoms are also very small,
so the atomic nucleus strongly attracts electrons.

Fluorine has the highest electronegativity of all elements
and strongly attracts electron density from other atoms.

In an F₂ molecule,
repulsion between the lone electron pairs on the two fluorine atoms is large,
so the F-F bond is not particularly strong.

On the other hand, many of the H-F bonds, C-F bonds,
and metal fluorides formed after reactions are extremely stable.

For these reasons, F₂ exhibits extremely high reactivity.

Hazards of Fluorine Gas

Fluorine gas F₂ is an extremely powerful oxidizing agent.

It reacts violently with many organic materials, metals,
reducing agents, and other substances,
and under certain conditions may cause ignition or explosions.

It is also highly toxic and corrosive,
and inhalation may cause serious damage to the respiratory system.

Because it also reacts with moisture,
contact with moisture in the eyes, respiratory tract, or skin
may also generate hydrogen fluoride.

Hazards of Hydrogen Fluoride and Hydrofluoric Acid

Hydrofluoric acid is highly corrosive,
but its hazards are not limited to ordinary acid chemical burns.

HF readily penetrates tissues,
and fluoride ions can bind to calcium ions
and magnesium ions in the body.

As a result, damage may extend beyond the skin surface
into deeper tissues.

Large exposures can also affect the electrolyte balance in the blood
and may lead to severe systemic symptoms.

Why Hydrofluoric Acid Corrodes Glass

The main component of ordinary glass
is silicon dioxide (SiO₂).

Hydrogen fluoride reacts with silicon
and forms fluorosilicon species,
allowing it to corrode glass.

This property is used not only in glass processing,
but also in semiconductor manufacturing
for etching processes that remove SiO₂ films.

What Is Hydrogen Fluoride Used For?

Hydrogen fluoride is not only used directly as a final product,
but also serves as a basic raw material
for producing many fluorine compounds.

Semiconductors

High-purity hydrofluoric acid is used
for cleaning silicon wafers
and etching SiO₂ films.

Fluoropolymers

Fluorine chemical raw materials are also used
to manufacture PTFE and other fluoropolymers,
fluororubbers, and various fluorine-based materials.

Refrigerants

Fluorine chemistry is also involved
in the production of various fluorinated refrigerants
used in air conditioners, refrigerators, and refrigeration equipment.

Glass Processing

The ability of HF to corrode SiO₂
is used for glass etching and surface treatment.

Metal Surface Treatment

Chemical solutions containing HF may also be used
for pickling and surface treatment of stainless steel and other metals.

Battery Materials

Fluorine chemistry is also involved
in the production of fluorine-based materials
used in lithium-ion batteries, such as LiPF₆.

What Is the “Fluoride” Used by Dentists?

When a dental clinic says that “fluoride is applied,”
this does not mean fluorine gas F₂
is being applied to the teeth.

High-concentration fluoride preparations
containing substances such as sodium fluoride are mainly used.

Professional fluoride application at dental clinics
uses fluoride at a much higher concentration
than household toothpaste.

However, only a small amount is used,
and it is applied to the tooth surface
under the supervision of dentists or dental hygienists.

Why Does Dental Fluoride Help Prevent Cavities?

When fluoride is present on the tooth surface,
it promotes remineralization,
in which calcium and phosphorus lost through tooth decay
return to the tooth.

It also makes the tooth surface more resistant to acid
and can suppress the activity of bacteria that cause tooth decay.

When high-concentration fluoride is applied,
calcium fluoride-like substances form on the tooth surface
and act as a temporary reservoir of fluoride.

How Much Does Fluoride Treatment at a Dentist Cost?

Fluoride application performed solely for prevention
rather than for the treatment of tooth decay
may be provided as private, non-insurance-covered treatment.

Fees vary by dental clinic,
but publicly listed examples include clinics
charging from several hundred yen to around 2,000 yen per treatment.

Subsidies may also be available
through municipal programs for infants and young children.

For example, under the fluoride application program
for eligible residents of Setagaya City, Tokyo,
the out-of-pocket cost is 880 yen.

What Is the Fluoride in Toothpaste?

Commercially sold “fluoride toothpaste”
also does not contain F₂ gas.

Representative fluoride compounds used include the following.

Medicated toothpastes sold in Japan
contain fluoride ion concentrations of no more than 1,500 ppmF.

High-fluoride toothpastes for adults
containing 1,450 ppmF are widely sold.

Recommended Fluoride Concentrations Differ by Age

According to recommendations published in 2023
by the Japanese Society for Oral Health,
Japanese Society of Pediatric Dentistry,
Japanese Society of Conservative Dentistry,
and Japanese Society of Gerodontology,
fluoride concentrations and amounts differ depending on age.

In particular, high-fluoride toothpaste
containing approximately 1,450 ppmF
is intended for people aged 6 and older in Japan.

How High Is the Fluoride Concentration in Toothpaste?

ppm means parts per million.

For example, toothpaste containing 1,450 ppmF
contains approximately 0.145% fluorine by weight.

Compared with the approximately 9,000 ppmF
used at dental clinics,
household toothpaste has a much lower concentration.

How Much Does Fluoride Toothpaste Cost?

Fluoride toothpaste is not particularly expensive,
and many ordinary commercially available toothpastes contain fluoride.

For example, some general-purpose toothpastes
containing 1,450 ppm fluoride and sold in 130 g tubes
are available for a few hundred yen.

Therefore, fluoride use at home
is very inexpensive when calculated on a per-use basis.

Is Fluoride Also Present in Tap Water?

Because fluoride compounds are also present in minerals and rocks,
natural water may contain small amounts of fluoride.

Therefore, depending on the water source,
tap water may naturally contain fluoride
even when fluoride has not been added artificially.

Fluoride Concentration in Japanese Tap Water

Japan has a drinking-water quality standard
for “fluorine and its compounds.”

Because 1 mg/L in an aqueous solution
is approximately equivalent to 1 ppm,
0.8 mg/L can be considered approximately 0.8 ppm.

What Is Community Water Fluoridation?

Community water fluoridation is a public health method
in which the fluoride concentration in drinking water
is adjusted to an appropriate level
for the purpose of preventing tooth decay.

The concept is to add fluoride when the natural fluoride concentration is low,
or conversely remove fluoride when it is too high,
in order to adjust it to an appropriate concentration.

The U.S. Public Health Service recommends
a fluoride concentration of 0.7 mg/L in drinking water
as a balance between preventing tooth decay
and the risk of dental fluorosis.

Does Japan Add Fluoride to Drinking Water for Cavity Prevention?

At present, community water fluoridation,
in which the fluoride concentration of an entire water supply
is adjusted for the purpose of preventing tooth decay,
is not practiced in Japan.

In the past, it was implemented
in the Yamashina district of Kyoto City from 1952 to 1965,
in Okinawa Prefecture from 1957 to 1972,
and in Asahi Town, Mie Prefecture, from 1967 to 1971.

Fluoride currently present in Japanese tap water
is basically naturally derived from water sources and other sources,
and is managed so that it remains within drinking-water quality standards.

What Is Added During Community Water Fluoridation?

In community water fluoridation overseas,
hazardous fluorine gas F₂
is not directly added to drinking water.

Representative fluoride compounds
used in water treatment facilities include the following.

In drinking water,
they ultimately exist as fluoride ions
at very low concentrations.

How Much Does Fluoride in Drinking Water Cost?

Because community water fluoridation
for the purpose of preventing tooth decay
is not currently practiced in Japan,
water users are not charged a separate
“fluoride addition fee.”

Naturally occurring fluoride is also included
in ordinary water charges,
and there is no separate charge for fluoride alone.

Community water fluoridation overseas
requires not only chemical costs,
but also dosing equipment, concentration measurement,
facility management, labor costs, and other expenses.

In U.S. economic evaluations,
one study reported annual community water fluoridation costs
ranging from approximately $0.11 to $4.89 per person.

Water systems serving larger populations
tend to have lower per-person costs.

Concentrations Differ Greatly Between Dental Treatment, Toothpaste, and Drinking Water

In this way, even though all of these are commonly referred to as “fluoride,”
the compounds used, concentrations, and methods of use differ greatly.

Why Should 9,000 ppm Dental Fluoride and 0.7 ppm Drinking Water Not Be Considered in the Same Way?

When considering the effects of a chemical substance,
it is necessary to consider not only what the substance is,
but also its concentration, amount used,
route of exposure, and duration of exposure.

Dental clinics use high-concentration preparations
containing approximately 9,000 ppmF,
but specialists apply only a small amount
to the tooth surface for a short period of time.

Toothpaste contains a lower concentration
of approximately 1,000–1,450 ppm
and is used for daily brushing.

Community water fluoridation, on the other hand,
uses a very low concentration of approximately 0.7 ppm.

However, dental fluoride preparations are not consumed like drinking water.
Therefore, the risk cannot be evaluated
simply by comparing ppm values.

What Happens If Too Much Fluoride Is Consumed?

Fluoride can be used to prevent cavities
when used at appropriate concentrations and in appropriate ways,
but excessive intake may cause undesirable effects.

In particular, prolonged excessive fluoride intake
during early childhood while teeth are developing
may cause dental fluorosis.

In mild cases,
white lines or spots may appear on the tooth surface.

Therefore, when children brush their teeth,
not only the fluoride concentration appropriate for their age
but also the amount of toothpaste used is important.

The Hazards of Fluorine Gas and the Fluoride in Toothpaste Are Completely Different

One of the most important points in understanding fluorine
is that substances containing the same element
do not necessarily have the same properties.

Just as chlorine gas Cl₂
and table salt NaCl have completely different properties,
fluorine gas F₂
and sodium fluoride NaF are also different substances.

Why Are Fluorine Compounds Useful?

While elemental fluorine F₂ is extremely reactive,
many compounds containing fluorine are extremely stable.

A representative example is the carbon-fluorine C-F bond.

Because the C-F bond is very strong,
fluoropolymers can have excellent properties
such as heat resistance, chemical resistance,
and low friction.

Fluorine chemistry is characterized
by using an extremely reactive element
to create extremely stable compounds.

Major Companies Manufacturing Hydrogen Fluoride

Hydrogen fluoride and high-purity hydrofluoric acid
are manufactured by fluorine chemical companies around the world.

Representative companies include
Honeywell, Solvay, Stella Chemifa,
Daikin Industries, LANXESS, and Koura.

Stella Chemifa

Stella Chemifa is one of Japan’s leading manufacturers
of high-purity fluorine compounds.

In particular, it handles high-purity hydrofluoric acid
for semiconductors and electronic materials.

Daikin Industries

Daikin Industries is not only an air-conditioning equipment manufacturer,
but also a major global fluorine chemical manufacturer.

It handles a wide range of products,
including fluoropolymers, fluororubbers,
and fluorinated intermediates.

Morita Chemical Industries

Morita Chemical Industries is a Japanese fluorine chemical manufacturer
that handles anhydrous hydrofluoric acid,
industrial hydrofluoric acid,
semiconductor-grade hydrofluoric acid,
ammonium fluoride, and other products.

Honeywell

Honeywell is a major U.S. company
that handles various fluorine chemical products,
including hydrogen fluoride.

Solvay

Solvay is also one of the world’s major
fluorine chemistry-related companies.

Koura

Koura is Orbia Group’s fluorine chemical business,
handling products ranging from fluorite
to hydrogen fluoride and downstream fluorine chemicals.

Hydrogen Fluoride Market Share

For hydrogen fluoride,
there are no official statistics
showing the latest company-by-company production volumes
for the entire global market under a single unified system.

In addition, because many manufacturers exist,
particularly in China,
estimated market shares vary among market research companies.

In one publicly available estimate for the 2021 market,
Stella Chemifa, Solvay, Honeywell,
Zhejiang Sanmei Chemical,
Daikin Industries, and others
were listed as major manufacturers.

Summary of Fluorine, Fluoride, and Hydrogen Fluoride

Summary

Fluorine is a halogen element
with the chemical symbol F and atomic number 9,
and in its elemental form it exists as the highly reactive gas F₂.

It is rarely found in elemental form in nature
and instead exists as stable fluoride compounds,
such as CaF₂ in fluorite.

Hydrogen fluoride HF produced from fluorite
is used across a wide range of modern industries,
including semiconductors, fluoropolymers, refrigerants,
glass processing, metal surface treatment,
and battery materials.

On the other hand, what is commonly called “fluoride”
in dental clinics and toothpaste
is not hazardous F₂ gas,
but mainly fluoride compounds such as sodium fluoride.

Concentrations differ greatly depending on the application,
with approximately 9,000 ppmF used at dental clinics,
approximately 1,450 ppmF in adult toothpaste,
and approximately 0.7 ppmF in community water fluoridation overseas.

Therefore, when considering whether “fluorine” is dangerous or safe,
it is important not to look only at the name of the element,
but to distinguish what type of compound it is,
what concentration is used,
and how it is used.