Keratin is a fibrous protein and has a helical structure, forming intermediate filaments, is tough and resistant to wear and tear, insoluble in water, rich in sulphur-containing amino acids, giving it strength and stability, as it forms disulfide bridges between cysteine residual groups, as well as hydrogen bonds, is the main component of hair, nails, and the outer layer of skin, providing protection against mechanical damage, contributes to the waterproofing of skin and feathers, as an impermeable barrier to water, preventing entry of water-borne pollutants.