Hair is not only aesthetically important in our culture, but also protects our scalp. This fiber-reinforced nanocomposite plays an important role in coating the outer skin of most vertebrates. Hair fibers have a characteristic hierarchical structure similar to other α-keratin materials such as nails and claws that are present in mammals. Keratin in reptiles and birds is found in the β form. Keratin-related materials are categorized as α-keratin with a helical secondary structure and β-keratin in the form of leaves. A characteristic fiber has a diameter of 50–100 μm and the outermost layer is covered by the cuticle. The cuticle is made up of thin overlapping plaques. Each plate has an average length of 60 μm and a thickness of 0.5 μm. The inner part of the hair consists of the cortex and cortical cells that are 100 μm long and 1–6 μm thick. These cortical cells are made up of subunits called macrofibrils. Macrofibrils have a diameter of 0.1–0.4 μm. Macrofibrils on the nanometer scale consist of intermediate filaments (IF) embedded in a high sulphide-content matrix. Each intermediate filament (IF) has a diameter of about 7.5 nm and consist of 8 protofilaments. Hair fibers consist of approximately 65-95% proteins, 32% water, lipid pigments and other components (Yang et al., 2016).
People have an average of 5 million hairs.