Keratín

Keratín, or keratin, is a family of fibrous structural proteins that form the main component of hair, nails, horns, claws, feathers, and the outermost layer of skin in vertebrates. Keratins belong to the intermediate filament protein family and are encoded by numerous KRT genes. They exist in two broad groups: soft keratins, which provide flexible protection in epithelia, and hard keratins, which are highly cross-linked and confer rigidity to hair, nails, and horn sheaths.

In cells, keratins assemble into intermediate filaments by pairing type I and type II keratins, creating a network that supports mechanical resilience and anchors intercellular junctions. Keratinocytes produce keratins as they differentiate in the epidermis; during keratinization, cytoplasm fills with keratin filaments and the cells become corneocytes, forming the protective outer skin layer.

In mammals, alpha-keratins predominate, whereas birds and reptiles rely on beta-keratins for the hard structures of feathers and claws. The diversity of keratin proteins—for example, through many KRT genes—enables tissue-specific filament networks. Mutations in keratin genes can cause keratinopathies, such as epidermolysis bullosa simplex and pachyonychia congenita, underscoring their essential role in epithelial integrity.

Keratin has various applications in cosmetics and biomedicine. It is used in some hair and skincare products and explored as a biomaterial for wound dressings, films, and scaffolds due to its biocompatibility and biodegradability. Extraction and processing methods vary, reflecting differences between hard and soft keratins and their intended uses.