"Keratinized" refers to a process where cells produce a tough, protective protein called keratin. This protein is a key component of the outer layer of skin, hair, and nails, providing strength and resilience. In keratinized tissues, cells become filled with keratin and eventually die, forming a durable barrier against environmental damage and pathogens. In humans, keratinized structures are most commonly found in the epidermis, the outermost layer of skin. This layer helps prevent water loss and protects underlying tissues from injury and infection. Keratinization is essential for maintaining healthy skin and is also observed in other animals, contributing to their protective features.