Keratin, << KEHR uh tihn, >> is a tough, insoluble protein found in the outer layer of the skin of human beings and many other animals. This outer layer of skin is called the epidermis. The outermost layer of cells of the epidermis contains keratin. The keratin in these cells makes the skin tough and almost completely waterproof. In places where the skin is exposed to much rubbing and pressure–such as parts of the hands and feet–the number of cells containing keratin increases and a callus develops. Cells that contain keratin are constantly being shed and replaced by new ones. The condition known as dandruff results when the scalp sheds such cells. See Dandruff .
Keratin is also a part of certain structures that grow from the skin. For example, the nails and hair of human beings contain keratin. In animals, such growths as horns, hoofs, claws, feathers, and scales consist mainly of keratin. Keratin helps make these structures stronger and better suited to protect the body from the environment.
