1. Cuticle: This is the outermost layer, composed of overlapping scales like shingles on a roof. It protects the inner layers from damage and helps hair to shine.
2. Cortex: This is the largest and strongest layer, making up the bulk of the hair shaft. It contains pigment granules that give hair its color, and it also determines the hair's texture (straight, wavy, curly).
3. Medulla: This is the innermost layer, which is not present in all hair types. It is a soft, hollow core that may be filled with air or a keratin-like substance. Its role is not fully understood, but it may provide some structural support.
These layers are all made up of a protein called keratin, which is also found in skin and nails. Keratin is made up of amino acids that are linked together in long chains. The arrangement of these chains and the presence of other molecules, like water and lipids, affect the properties of the hair, such as its strength, elasticity, and texture.