Hair and teeth are prominent external structures of the human body. While they share some fundamental biological origins and building blocks, they are not made of the exact same material. Their distinct compositions enable them to perform their very different functions within the body.
The Makeup of Hair
Hair is primarily a protein filament emerging from follicles in the skin. The main component of human hair is a tough protein known as keratin, which also forms fingernails and toenails. Each strand of hair is composed of dead, keratinized cells.
A hair shaft consists of three main layers: the cuticle, cortex, and medulla. The outermost layer, the cuticle, is made of overlapping cells resembling roof shingles, providing protection and shine. Beneath this is the cortex, the thickest layer, which contains keratin bundles and melanin, the pigment responsible for hair color. The innermost layer, the medulla, is an unstructured region that is not always present. The type and amount of melanin determine human hair colors.
The Composition of Teeth
Human teeth are complex structures made of four distinct types of tissue: enamel, dentin, pulp, and cementum. The enamel is the hard, protective outer layer of the tooth crown, serving as the hardest substance in the human body. It is predominantly composed of hydroxyapatite crystals, a calcium phosphate mineral.
Beneath the enamel lies the dentin, a bone-like tissue that forms the bulk of the tooth. While also mineralized with hydroxyapatite, dentin is softer than enamel and contains a higher proportion of organic matter. The pulp, located at the tooth’s core, is a soft tissue containing nerves, blood vessels, and connective tissue, which supply nutrients and sensory perception to the tooth. Covering the tooth root is the cementum, a calcified tissue that helps anchor the tooth to the jawbone through the periodontal ligament.
Comparing Hair and Teeth
Hair and teeth, despite their apparent differences, share an embryonic origin from the ectoderm. Both are biological structures that contain proteins as fundamental building blocks. While hair is primarily keratin, recent research suggests that specific hair keratins may be present in the organic fraction of tooth enamel, potentially influencing its structure and resistance to decay.
The most significant differences lie in their primary composition and physical properties. Hair is predominantly made of the protein keratin, making it flexible, elastic, and capable of continuous growth. It serves functions such as protection from UV rays, insulation, and sensory input. In contrast, teeth are primarily composed of highly mineralized tissues, particularly enamel’s hydroxyapatite, which provides rigidity and hardness. Unlike hair, teeth do not grow continuously once fully formed, and enamel cannot regenerate if damaged; their rigid, durable composition is adapted for mechanical functions like biting, tearing, and grinding food.