+Keratin is a [fibrous protein](/wiki/fibrous-protein) and the primary building block of tough, protective outer layers in many animals. It forms the core structure of [hair](/wiki/hair), nails, feathers, and the outer layer of skin, providing strength and resilience.
+## See also
+- [Protein](/wiki/protein)
+- [Skin](/wiki/skin)
+- [Nail](/wiki/nail)
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