Adequate fluoride intake is beneficial for oral health in both children and adults. It prevents tooth decay through various mechanisms. Fluoride in low concentrations in saliva and plaque delays demineralization and accelerates remineralization of enamel lesions. It also disrupts glycolysis, the process by which cariogenic bacteria metabolize sugars to produce acid, and has bactericidal effects on these and other bacteria. During tooth development, ingested fluoride makes enamel more resistant to acid attacks and caries formation. However, excessive fluoride intake can be harmful. High amounts can bind to calcium, interfering with proteolytic and glycolytic enzyme activities. Fluoride ingestion in large quantities can be toxic, causing reactions with gastric acid to form hydrofluoric acid, which leads to abdominal pain, excessive salivation, nausea, vomiting, seizures, muscle cramps, and potentially respiratory paralysis. Inhalation of hydrogen fluoride can severely irritate the respiratory tract, cause asthma-like reactions, and pulmonary edema, while skin or eye contact can result in severe burns. Exposure to aluminium fluoride, particularly in occupational settings, can be fatal and may cause asthma with prolonged exposure.