keratinisation

Keratinisation, also known as cornification, is a biological process where cells fill with a tough, protective protein called keratin and eventually die. This process is a fundamental aspect of the development and function of the epidermis, the outermost layer of the skin in mammals, as well as the formation of structures like hair, nails, and feathers in other animals.

The process begins in the deepest layer of the epidermis, the stratum basale. Cells in this layer, called keratinocytes, are actively dividing. As they move upwards towards the surface, they undergo significant changes. They start producing increasing amounts of keratin. Simultaneously, their organelles, such as the nucleus and mitochondria, degenerate.

As the keratinocytes reach the stratum corneum, the outermost layer of the epidermis, they are essentially dead, flattened sacs filled almost entirely with keratin. These dead cells are constantly shed from the surface and replaced by new cells from below. This continuous shedding and renewal is crucial for maintaining the skin's barrier function, protecting the body from physical damage, dehydration, and invasion by pathogens. The degree and pattern of keratinisation can vary depending on the location on the body and the specific physiological needs.