Keratin is a fibrous structural protein found in the outermost layers of the epidermis, hair, nails, feathers, hooves, and horns of animals. It is an essential component of many biological materials due to its toughness and protective properties.

In human biology, keratin plays a significant role in the structure of the skin, forming a barrier that helps protect the body from environmental damage and dehydration. It also contributes to the structure of hair and nails, making them strong and resilient. The human epidermis consists of multiple layers, and keratinocytes, which are skin cells, produce keratin as they move to the skin’s surface. These keratinized skin cells eventually become the tough, outermost layer of the epidermis, providing protection and waterproofing.

Keratin is also found in the hair, giving it its strength and structure. Hair strands are primarily composed of keratin protein, and the type and arrangement of keratin determine the texture and appearance of hair.

In addition to humans, many other animals, such as birds, reptiles, and mammals, have keratin in their bodies. For example, in birds, keratin makes up the feathers, while in reptiles, it forms scales. In animals like cows and horses, keratin is a major component of hooves and horns.