Fluoride is safe and effective when used properly. However, some risks have been associated with exposure to high levels of fluoride for prolonged periods of time. These include:

• Dental fluorosis. Most commonly involves minor discoloration of tooth enamel, such as the appearance of white or opaque lines, streaks or spots. In severe cases, the discoloration may appear as brown, black or gray spots, and the enamel may become pitted or misshapen. Fluorosis is cosmetic and only affects the tooth’s surface. It is a permanent condition, and discoloration generally darkens as a person ages. Fluorosis may be treated by teeth whitening, bonding, crowns or veneers.
  
  Fluorosis occurs in children whose teeth are still developing. Once teeth have erupted in the mouth, they are no longer susceptible to fluorosis. Most cases of fluorosis occur when children take fluoride supplements (or swallow large amounts of fluoride toothpaste or mouth rinse) in addition to receiving adequate levels of fluoride in their drinking water. Some children develop fluorosis due to naturally high levels of fluoride in their drinking water. Fluoride treatments are not likely to contribute to fluorosis due to the relative infrequency of these professional applications.
  
  
• Bone weakening. A lifetime exposure to high levels of fluoride has been found to increase bone density, but not necessarily strength. Animal studies and several studies on the effect of fluoride in humans have shown an association with increased brittleness of bone. However, more research is needed to conclusively identify fluoride as the cause of this increased risk of bone fracture.
  
  
• Skeletal fluorosis. A disorder of the bones and joints associated with prolonged exposure to high levels of fluoride. It can cause joint stiffness and pain. Scientific evidence is inconclusive about the relationship between fluoride and skeletal fluorosis, and more research is needed. This is an extremely rare condition in the United States. 

Chronic exposure to high levels of fluoride may worsen certain existing medical conditions, such as joint pain, kidney problems and stomach ulcers. At this time, there is no conclusive evidence linking high levels of fluoride with cancer (e.g., bone cancer). Research continues in this area.

Allergic reactions to fluoride may occur in a small number of cases. Very small amounts of fluoride may pass into breastmilk, but no problems have been associated in children whose mothers consumed recommended levels of fluoride while pregnant or breastfeeding. 

Fluoride overdose may occur when large concentrations of fluoride are consumed at once. For example, small children who swallow large amounts of fluoride toothpaste (e.g., an entire tube by a small child) or fluoride mouth rinse, or take an overdose of fluoride supplements, may consume toxic levels of fluoride.

Toxic effects of fluoride will depend on the person’s age, weight and amount of fluoride consumed. For example, 320 milligrams (mg) of fluoride will have a toxic effect on a 2-year-old who weighs 22 pounds (10 kilograms [kg]). About 655 mg of fluoride may be toxic to an 8-year-old who weighs 45 pounds (20 kg). If medical attention is not received immediately, death may occur.  

Symptoms of fluoride overdose include:

• Nausea
• Vomiting (may include blood)
• Diarrhea (stool may be black, tarry)
• Abdominal pain
• Excessive salivation
• Watery eyes
• Weakness
• Shallow breathing
• Faintness
• Drowsiness
• Tremors, convulsions

Medical attention should be sought immediately for the above symptoms. If fluoride overdose is suspected, drinking milk may slow the absorption of fluoride in the body.

Any concerns about fluoride use should be brought to the attention of a dentist or physician. In addition, a local poison control center or the national poison control hotline (1-800-222-1222) can provide information about fluoride use and possible overdose.