Tooth enamel is the hard, outer layer of a tooth that protects it from decay and damage. It is the hardest substance in the human body, primarily composed of minerals, mainly hydroxyapatite. Enamel serves as a barrier against acids and bacteria that can lead to cavities. Although tooth enamel is strong, it can wear down over time due to factors like poor oral hygiene, acidic foods, and grinding teeth. Once enamel is lost, it cannot regenerate, making it essential to maintain good dental care practices to preserve this protective layer.