Fluoride Action Network

WHO: Fluorosis

Source: World Health Organization | November 24th, 2019
Location: International

The disease and how it affects people

Ingestion of excess fluoride, most commonly in drinking-water, can cause fluorosis which affects the teeth and bones. Moderate amounts lead to dental effects, but long-term ingestion of large amounts can lead to potentially severe skeletal problems. Paradoxically, low levels of fluoride intake help to prevent dental caries. The control of drinking-water quality is therefore critical in preventing fluorosis. The condition and its effect on people Fluorosis is caused by excessive intake of fluoride. The dental effects of fluorosis develop much earlier than the skeletal effects in people exposed to large amounts of fluoride. Clinical dental fluorosis is characterized by staining and pitting of the teeth. In more severe cases all the enamel may be damaged. However, fluoride may not be the only cause of dental enamel defects. Enamel opacities similar to dental fluorosis are associated with other conditions, such as malnutrition with deficiency of vitamins D and A or a low protein-energy diet. Ingestion of fluoride after six years of age will not cause dental fluorosis.

Chronic high-level exposure to fluoride can lead to skeletal fluorosis. In skeletal fluorosis, fluoride accumulates in the bone progressively over many years. The early symptoms of skeletal fluorosis, include stiffness and pain in the joints. In severe cases, the bone structure may change and ligaments may calcify, with resulting impairment of muscles and pain.

Acute high-level exposure to fluoride causes immediate effects of abdominal pain, excessive saliva, nausea and vomiting. Seizures and muscle spasms may also occur.

The cause

Acute high-level exposure to fluoride is rare and usually due to accidental contamination of drinking-water or due to fires or explosions. Moderate-level chronic exposure (above 1.5 mg/litre of water – the WHO guideline value for fluoride in water) is more common. People affected by fluorosis are often exposed to multiple sources of fluoride, such as in food, water, air (due to gaseous industrial waste), and excessive use of toothpaste. However, drinking water is typically the most significant source. A person’s diet, general state of health as well as the body’s ability to dispose of fluoride all affect how the exposure to fluoride manifests itself.


Fluoride in water is mostly of geological origin. Waters with high levels of fluoride content are mostly found at the foot of high mountains and in areas where the sea has made geological deposits. Known fluoride belts on land include: one that stretches from Syria through Jordan, Egypt, Libya, Algeria, Sudan and Kenya, and another that stretches from Turkey through Iraq, Iran, Afghanistan, India, northern Thailand and China. There are similar belts in the Americas and Japan. In these areas fluorosis has been reported.

Scope of the Problem

The prevalence of dental and skeletal fluorosis is not entirely clear. It is believed that fluorosis affects millions of people around the world, but as regards dental fluorosis the very mild or mild forms are the most frequent.


Removal of excessive fluoride from drinking-water is difficult and expensive. The preferred option is to find a supply of safe drinking-water with safe fluoride levels. Where access to safe water is already limited, de-fluoridation may be the only solution. Methods include: use of bone charcoal, contact precipitation, use of Nalgonda or activated alumina (Nalgonda is called after the town in South India, near Hyderabad, where the aluminium sulfate-based defluoridation was first set up at a water works level). Since all methods produce a sludge with very high concentration of fluoride that has to be disposed of, only water for drinking and cooking purposes should be treated, particularly in the developing countries.

Health education regarding appropriate use of fluorides.

Mothers in affected areas should be encouraged to breastfeed since breast milk is usually low in fluoride.


World Health Organization. Guidelines for drinking-water quality. Vol. 1. Geneva, 1993 (Second edition)

World Health Organization. Guidelines for drinking-water quality. Vol. 2. Geneva, 1999 (Second edition)

Fluoride in drinking-water, WHO/IWA (in preparation)

Prepared for World Water Day 2001. Reviewed by staff and experts from Oral Health Programme (ORH), and Water, Sanitation and Health Programme (WSH), World Health Organization (WHO), Geneva.

*Online as of November 24, 2019, at https://www.who.int/water_sanitation_health/diseases-risks/diseases/fluorosis/en/


This article is also accessible under Government Reports, in the Researchers section, under World Health Organization | United Nations at https://www.who.int/water_sanitation_health/diseases-risks/diseases/fluorosis/en/