<P> Keratin (/ ˈkɛrətɪn /) is one of a family of fibrous structural proteins . It is the key structural material making up hair, horns, claws, hooves, and the outer layer of human skin . Keratin is also the protein that protects epithelial cells from damage or stress . Keratin is extremely insoluble in water and organic solvents . Keratin monomers assemble into bundles to form intermediate filaments, which are tough and form strong unmineralized epidermal appendages found in reptiles, birds, amphibians, and mammals . The only other biological matter known to approximate the toughness of keratinized tissue is chitin . </P> <P> Keratin derives from Greek κερατίνη from Greek keras (κέρας) (genitive keratos, κέρατος) meaning "horn" originating from the Proto - Indo - European * ḱer - of the same meaning . It is composed of "horn like", i.e., kerato, to which the chemical suffix - in is appended . The Greek keras (or keros) is used in many animal names, e.g. Rhinoceros, meaning "nose with a horn". </P>

What is the role of keratin in the skin