Keratin
Definition
Keratin is a tough, fibrous structural protein that is the primary component of the outermost layer of skin (stratum corneum), as well as hair and nails. In the skin, keratin forms a protective shield that resists environmental damage, prevents water loss, and provides mechanical strength. Keratinocytes, the main cells of the epidermis, produce keratin as they migrate from the basal layer to the surface, eventually becoming the flattened, dead, keratin-filled cells (corneocytes) that make up the stratum corneum. There are different types of keratin — the soft keratin in skin is more flexible than the hard keratin in nails. When keratin production is disrupted or excessive, conditions like keratosis pilaris (rough, bumpy skin on the arms and legs) or calluses can develop. Chemical exfoliants and enzyme treatments help manage excess keratin buildup by dissolving or loosening the protein.
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