Keratinization is the process by which keratin hardens. Keratin is a protein found in the outer layer of the skin, hair, and nails, notes Healthline. This protein protects the skin through keratinization.
Without keratinization, the skin would easily break, which could result in frequent infection. Keratin hardens as keratinocytes, found in epithelial cells, produce more and more keratin. According to Healthline, the keratin forms a tight mesh, making it impenetrable unless damaged. As these keratinized cells age on the skin, the body sloughs off the dead or damaged cells.
In nails, the keratinocytes continue to produce keratin at the base of the nail, resulting in ever-lengthening nails. As the nail becomes longer, people either clip them, or eventually through everyday tasks, the nail chips and breaks off. In hair, keratinization occurs as the hair shaft lengthens and moves away from its source of nutrients. The outer layer of the hair, the cuticle, is composed of keratin that begins to harden to protect the hair shaft from injury, explains KidsHealth. Keratinization occurs slightly differently in skin, nails and hair, but the general process and purpose are the same. The same mesh-like outer layer is formed on the skin, nails and hair to protect them from damage and potential foreign invaders like bacteria.