Hard keratins are a type of fibrous protein found in various structures of the body, primarily in hair, nails, and the outer layer of skin. They provide strength and resilience, making these structures durable and protective against environmental damage. Hard keratins are characterized by their high sulfur content, which contributes to their toughness and rigidity. These proteins are different from soft keratins, which are more flexible and found in tissues like the inner layers of the skin. Hard keratins play a crucial role in maintaining the integrity of epithelial tissues, helping to prevent water loss and protect against pathogens.