Keratin refers to a family of fibrous structural proteins. Keratin is the key structural material making up the outer layer of human skin. It is also the key structural component of hair and nails. Keratin monomers assemble into bundles to form intermediate filaments, which are tough and insoluble and form strong unmineralized tissues found in reptiles, birds, amphibians, and mammals. The only other biological matter known to approximate the toughness of Keratinized tissue is chitin.
Keratin is a popular strengthening additive in high-quality hair and skin care products. It is a natural fibrous protein that can be used in shampoos, conditioners and various lotions.